R FAQ

R FAQ

Frequently Asked Questions on R

Version 0.90-2, 1999/11/25

Kurt Hornik


Table of Contents


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Node:Introduction, Next:, Previous:Top, Up:Top

1 Introduction

This document contains answers to some of the most frequently asked questions about R.


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1.1 Legalese

This document is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version.

This document is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

A copy of the GNU General Public License is available via WWW at

http://www.gnu.org/copyleft/gpl.html.

You can also obtain it by writing to the Free Software Foundation, Inc., 59 Temple Place -- Suite 330, Boston, MA 02111-1307, USA.


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1.2 Obtaining this document

The latest version of this document is always available from

http://www.ci.tuwien.ac.at/~hornik/R/

From there, you can obtain versions converted to plain ASCII text, DVI, GNU info, HTML, PDF, PostScript as well as the Texinfo source used for creating all these formats using the GNU Texinfo system.

You can also obtain the R FAQ from the doc/FAQ subdirectory of a CRAN site (What is CRAN?).


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1.3 Citing this document

In publications, please refer to this FAQ as Hornik (1999), "The R FAQ" and give the above, official URL.


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1.4 Notation

Everything should be pretty standard. R> is used for the R prompt, and a $ for the shell prompt (where applicable).


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1.5 Feedback

Feedback is of course most welcome.

In particular, note that I do not have access to Windows or Mac systems. Features specific to the Windows port of R are described in the "Frequently Asked Questions for R for Windows". If you have information on Windows or Mac systems that you think should be added to this document, please let me know.


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2 R Basics


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2.1 What is R?

R is a system for statistical computation and graphics. It consists of a language plus a run-time environment with graphics, a debugger, access to certain system functions, and the ability to run programs stored in script files.

The design of R has been heavily influenced by two existing languages: Becker, Chambers & Wilks' S (see What is S?) and Sussman's Scheme. Whereas the resulting language is very similar in appearance to S, the underlying implementation and semantics are derived from Scheme. See What are the differences between R and S?, for a discussion of the differences between R and S.

R was initially written by Ross Ihaka and Robert Gentleman, who are Senior Lecturers at the Department of Statistics of the University of Auckland in Auckland, New Zealand. In addition, a large group of individuals has contributed to R by sending code and bug reports.

Since mid-1997 there has been a core group (the "R Core Team") who can modify the R source code CVS archive. The group currently consists of Doug Bates, Peter Dalgaard, Robert Gentleman, Kurt Hornik, Ross Ihaka, Friedrich Leisch, Thomas Lumley, Martin Maechler, Guido Masarotto, Paul Murrell, Brian Ripley, Duncan Temple Lang, and Luke Tierney.

R has a home page at http://stat.auckland.ac.nz/r/r.html. It is free software distributed under a GNU-style copyleft, and an official part of the GNU project ("GNU S").


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2.2 What machines does R run on?

R is being developed for the Unix, Windows and Mac families of operating systems.

The current version of R will configure and build under a number of common Unix platforms including i386-freebsd, i386-linux, ppc-linux, mips-sgi-irix, alpha-linux, alpha-dec-osf4, rs6000-ibm-aix, hppa-hp-hpux, sparc-linux, and sparc-sun-solaris, see the file PLATFORMS in the R distribution for more information.

If you know about other platforms, please drop us a note.


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2.3 What is the current version of R?

The current stable Unix/Windows version is 0.90.0, the unstable one is 0.99.0. Typically, new features are introduced in the development versions; updates of stable versions are for bug fixes mostly. The version for the Mac is pre-alpha.


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2.4 How can R be obtained?

Sources, binaries and documentation for R can be obtained via CRAN, the "Comprehensive R Archive Network" (see What is CRAN?).


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2.5 How can R be installed?


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2.5.1 How can R be installed (Unix)

If binaries are available for your platform (see Are there Unix binaries for R?), you can use these, following the instructions that come with them.

Otherwise, you can compile and install R yourself, which can be done very easily under a number of common Unix platforms (see What machines does R run on?). The file INSTALL that comes with the R distribution contains instructions.

Note that you need a FORTRAN compiler or f2c in addition to a C compiler to build R. Also, you need Perl version 5 to build the documentation. If this is not available on your system, you can obtain precompiled documentation files via CRAN.

In the simplest case, untar the R source code, cd to the directory thus created, and issue the following commands (at the shell prompt):

$ ./configure
$ make

If these commands execute successfully, the R binary and a shell script font-end called R are created and copied to the bin directory. You can copy the script to a place where users can invoke it, for example to /usr/local/bin. In addition, plain text help pages as well as HTML and LaTeX versions of the documentation are built.

Use make dvi to obtain a dvi version of the R manual. This creates the files Manual.dvi (a start of a manual) and Reference.dvi (an R object reference index) in the doc/manual subdirectory. These files can be previewed and printed using standard programs such as xdvi and dvips. (Note that they have to be built in the source tree.)

Finally, use make check to find out whether your R system works correctly.

You can also perform a "system-wide" installation using make install. By default, this will install to the following directories:

${prefix}/bin
(some) executables
${prefix}/man/man1
man pages
${prefix}/share/R
all the rest (libraries, on-line help system, ...). This is the "R Home Directory" (R_HOME) of the installed system.

In the above, prefix is determined during configuration (typically /usr/local) and can be set by running configure with the option

$ ./configure --prefix=/where/you/want/R/to/go

(E.g., the R executable will then be installed into /where/you/want/R/to/go/bin.)


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2.5.2 How can R be installed (Windows)

The bin/windows/windows-NT directory of a CRAN site contains the latest binary distributions of R for 32 bit versions of MS Windows (i.e., 95, 98 or NT), as well as binary distributions for a large number of add-on packages from CRAN. The Windows version of R was created by Robert Gentleman, and is now being developed and maintained by Guido Masarotto and Brian D. Ripley.

For most installations the installer rwinst.exe will be the easiest tool to use.

See the R Windows FAQ for more details.


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2.5.3 How can R be installed (Macintosh)

The Power Macintosh port is temporarily on hold, and currently no binary distribution is available. We hope that this will change soon.


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2.6 Are there Unix binaries for R?

The bin/linux directory contains Debian 2.1 packages for the i386 platform (now part of the Debian distribution and maintained by Doug Bates) as well as Red Hat 5.1 packages for the alpha and sparc platforms (maintained by Nassib Nasser and Vin Everett, respectively), Red Hat 6.0 packages for the i386 and alpha platforms (maintained by Martyn Plummer and Naoki Takebayashi, respectively), S.u.S.E. 5.3/6.0/6.2 i386 packages by Albrecht Gebhardt, and RPMs for the ppc platform by Alex Buerkle.

The bin/osf directory contains RPMs for alpha systems running Digital Unix 4.0 by Albrecht Gebhardt.

No other binary distributions have thus far been made publically available.


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2.7 What documentation exists for R?

Online documentation for most of the functions and variables in R exists, and can be printed on-screen by typing help(name) (or ?name) at the R prompt, where name is the name of the topic help is sought for. (In the case of unary and binary operators and control-flow special forms, the name may need to be be quoted.)

This documentation can also be made available as HTML, and as hardcopy via LaTeX, see How can R be installed?. An up-to-date HTML version is always available for web browsing at http://stat.ethz.ch/R/manual/.

An earlier attempt at an R manual ("Notes on R: A Programming Environment for Data Analysis and Graphics"), based on the "Notes on S-PLUS" by Bill Venables and David Smith, can be obtained as Rnotes.tgz (LaTeX source) in a CRAN doc directory. Further documentation on R and the R API are currently being written.

In the absence of an R manual, documentation for S/S-PLUS (see R and S) can be used in combination with this FAQ (see What are the differences between R and S?). We recommend

W. N. Venables and B. D. Ripley (1999), "Modern Applied Statistics with S-PLUS. Third Edition". Springer, ISBN 0-387-98825-4.

which has a home page at http://www.stats.ox.ac.uk/pub/MASS3/ providing additional material, in particular "R Complements" which describe how to use the book with R. These complements provide both descriptions of some of the differences between R and S-PLUS, and the modifications needed to run the examples in the book. Its companion volume on "S Programming", due in about April 2000, will provide an in-depth guide to writing software in the S language which forms the basis of both the commercial S-PLUS and the Open Source R data analysis software systems.

More introductory books are

P. Spector (1994), "An introduction to S and S-PLUS", Duxbury Press.

A. Krause and M. Olsen (1997), "The Basics of S and S-PLUS", Springer.

Last, but not least, Ross' and Robert's experience in designing and implementing R is described in:

@article{,
  author =    {Ross Ihaka and Robert Gentleman},
  title =     {R: A Language for Data Analysis and Graphics},
  journal =   {Journal of Computational and Graphical Statistics},
  year =      1996,
  volume =    5,
  number =    3,
  pages =     {299--314}
}


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2.8 Citing R

To cite R in publications, use the above Ihaka & Gentleman (1996), "R: A Language for Data Analysis and Graphics", Journal of Computational and Graphical Statistics, 5, 299-314.


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2.9 What mailing lists exist for R?

Thanks to Martin Maechler, there are three mailing lists devoted to R.

r-announce
This list is for announcements about the development of R and the availability of new code.
r-devel
This list is for discussions about the future of R and pre-testing of new versions. It is meant for those who maintain an active position in the development of R.
r-help
The `main' R mailing list, for announcements about the development of R and the availability of new code, questions and answers about problems and solutions using R, enhancements and patches to the source code and documentation of R, comparison and compatibility with S and S-PLUS, and for the posting of nice examples and benchmarks.

Note that the r-announce list is gatewayed into r-help, so you don't need to subscribe to both of them.

Send email to r-help@lists.r-project.org to reach everyone on the r-help mailing list. To subscribe (or unsubscribe) to this list send subscribe (or unsubscribe) in the BODY of the message (not in the subject!) to r-help-request@lists.r-project.org. Information about the list can be obtained by sending an email with info as its contents to r-help-request@lists.r-project.org.

Subscription and posting to the other lists is done analogously, with `r-help' replaced by `r-announce' and `r-devel', respectively.

It is recommended that you send mail to r-help rather than only to the R developers (who are also subscribed to the list, of course). This may save them precious time they can use for constantly improving R, and will typically also result in much quicker feedback for yourself.

Of course, in the case of bug reports it would be very helpful to have code which reliably reproduces the problem. Also, make sure that you include information on the system and version of R being used. See R Bugs for more details.

Archives of the above three mailing lists are made available on the net in a monthly schedule via the doc/mail/mail.html file in CRAN. An HTML archive of the lists are available via http://www.ens.gu.edu.au/robertk/R/.

The R Core Team can be reached at r-core@lists.r-project.org for comments and reports.


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2.10 What is CRAN?

The "Comprehensive R Archive Network" (CRAN) is a collection of sites which carry identical material, consisting of the R distribution(s), the contributed extensions, documentation for R, and binaries.

The CRAN master site can be found at the URL

http://cran.r-project.org/ (Austria)

(which is the same as http://cran.at.r-project.org/) and is currently being mirrored daily at

http://cran.dk.r-project.org/ (Denmark)
http://cran.it.r-project.org/ (Italy)
http://cran.ch.r-project.org/ (Switzerland)
http://cran.uk.r-project.org/ (United Kingdom)
http://cran.us.r-project.org/ (USA/Wisconsin)

Please use the CRAN site closest to you to reduce network load.

From CRAN, you can obtain the latest official release of R, daily snapshots of R (copies of the current CVS trees), as gzipped and bzipped tar files or as two gzipped tar files (ready for 1.4M floppies), a wealth of additional contributed code, as well as prebuilt binaries for various operating systems (Linux, Nextstep, MacOS, MSWin) and pre-formatted help pages. CRAN also provides access to documentation on R, existing mailing lists and the R Bug Tracking system.

To "submit" to CRAN, simply upload to ftp://cran.r-project.org/incoming and send an email to wwwadmin@cran.r-project.org.

Note: It is very important that you indicate the copyright (license) information (GPL, BSD, Artistic, ...) in your submission.

Please always use the URL of the master site when referring to CRAN.


Node:R and S, Next:, Previous:R Basics, Up:Top

3 R and S


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3.1 What is S?

S is a very high level language and an environment for data analysis and graphics. S was written by Richard A. Becker, John M. Chambers, and Allan R. Wilks of AT&T Bell Laboratories Statistics Research Department.

The primary references for S are two books by the creators of S.

Version 4 of S, a major revision of S designed by John Chambers to improve its usefulness at every stage of the programming process, is described in "Programming with Data" by John M. Chambers (1998), Springer: New York, ISBN 0-387-98503-4.

In 1998, the Association for Computing Machinery presented its Software System Award to John Chambers for the design of the S system. The ACM citation stated that "S has forever altered the way people analyze, visualize, and manipulate data .... S is an elegant, widely accepted, and enduring software system, with conceptual integrity, thanks to the insight, taste, and effort of John Chambers." See http://netlib.bell-labs.com/cm/ms/departments/sia/S/index.html for "Stages in the Evolution of S".

There is a huge amount of user-contributed code for S, available at the S Repository at CMU.

The "Frequently Asked Questions about S" contains further information about S, but is not up-to-date.


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3.2 What is S-PLUS?

S-PLUS is a value-added version of S sold by Statistical Sciences, Inc. (now a division of Mathsoft, Inc.). Based on the S language, S-PLUS provides functionality in a wide variety of areas, including robust regression, modern non-parametric regression, time series, survival analysis, multivariate analysis, classical statistical tests, quality control, and graphics drivers. Add-on modules add additional capabilities for wavelet analysis, spatial statistics, GARCH models, and design of experiments.

See the MathSoft S-PLUS page for further information.


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3.3 What are the differences between R and S?


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3.3.1 Lexical scoping

Whereas the developers of R have tried to stick to the S language as defined in "The New S Language" (Blue Book, see What is S?), they have adopted the evaluation model of Scheme.

This difference becomes manifest when free variables occur in a function. Free variables are those which are neither formal parameters (occurring in the argument list of the function) nor local variables (created by assigning to them in the body of the function). Whereas S (like C) by default uses static scoping, R (like Scheme) has adopted lexical scoping. This means the values of free variables are determined by a set of global variables in S, but in R by the bindings that were in effect at the time the function was created.

Consider the following function:

cube <- function(n) {
  sq <- function() n * n
  n * sq()
}

Under S, sq() does not "know" about the variable n unless it is defined globally:

S> cube(2)
Error in sq():  Object "n" not found
Dumped
S> n <- 3
S> cube(2)
[1] 18

In R, the "environment" created when cube() was invoked is also looked in:

R> cube(2)
[1] 8

As a more "interesting" real-world problem, suppose you want to write a function which returns the density function of the r-th order statistic from a sample of size n from a (continuous) distribution. For simplicity, we shall use both the cdf and pdf of the distribution as explicit arguments. (Example compiled from various postings by Luke Tierney.)

The S-PLUS documentation for call() basically suggests the following:

dorder <- function(n, r, pfun, dfun) {
  f <- function(x) NULL
  con <- round(exp(lgamma(n + 1) - lgamma(r) - lgamma(n - r + 1)))
  PF <- call(substitute(pfun), as.name("x"))
  DF <- call(substitute(dfun), as.name("x"))
  f[[length(f)]] <-
    call("*", con,
         call("*", call("^", PF, r - 1),
              call("*", call("^", call("-", 1, PF), n - r),
                   DF)))
  f
}

Rather tricky, isn't it? The code uses the fact that in S, functions are just lists of special mode with the function body as the last argument, and hence does not work in R (one could make the idea work, though).

A version which makes heavy use of substitute() and seems to work under both S and R is

dorder <- function(n, r, pfun, dfun) {
  con <- round(exp(lgamma(n + 1) - lgamma(r) - lgamma(n - r + 1)))
  eval(substitute(function(x) K * PF(x)^a * (1 - PF(x))^b * DF(x),
                  list(PF = substitute(pfun), DF = substitute(dfun),
                       a = r - 1, b = n - r, K = con)))
}

(the eval() is not needed in S).

However, in R there is a much easier solution:

dorder <- function(n, r, pfun, dfun) {
  con <- round(exp(lgamma(n + 1) - lgamma(r) - lgamma(n - r + 1)))
  function(x) {
    con * pfun(x)^(r - 1) * (1 - pfun(x))^(n - r) * dfun(x)
  }
}

This seems to be the "natural" implementation, and it works because the free variables in the returned function can be looked up in the defining environment (this is lexical scope).

Note that what you really need is the function closure, i.e., the body along with all variable bindings needed for evaluating it. Since in the above version, the free variables in the value function are not modified, you can actually use it in S as well if you abstract out the closure operation into a function MC() (for "make closure"):

dorder <- function(n, r, pfun, dfun) {
  con <- round(exp(lgamma(n + 1) - lgamma(r) - lgamma(n - r + 1)))
  MC(function(x) {
       con * pfun(x)^(r - 1) * (1 - pfun(x))^(n - r) * dfun(x)
     },
     list(con = con, pfun = pfun, dfun = dfun, r = r, n = n))
}

Given the appropriate definitions of the closure operator, this works in both R and S, and is much "cleaner" than a substitute/eval solution (or one which overrules the default scoping rules by using explicit access to evaluation frames, as is of course possible in both R and S).

For R, MC() simply is

MC <- function(f, env) f

(lexical scope!), a version for S is

MC <- function(f, env = NULL) {
  env <- as.list(env)
  if (mode(f) != "function")
    stop(paste("not a function:", f))
  if (length(env) > 0 && any(names(env) == ""))
    stop(paste("not all arguments are named:", env))
  fargs <- if(length(f) > 1) f[1:(length(f) - 1)] else NULL
  fargs <- c(fargs, env)
  if (any(duplicated(names(fargs))))
    stop(paste("duplicated arguments:", paste(names(fargs)),
         collapse = ", "))
  fbody <- f[length(f)]
  cf <- c(fargs, fbody)
  mode(cf) <- "function"
  return(cf)
}

Similarly, most optimization (or zero-finding) routines need some arguments to be optimized over and have other parameters that depend on the data but are fixed with respect to optimization. With R scoping rules, this is a trivial problem; simply make up the function with the required definitions in the same environment and scoping takes care of it. With S, one solution is to add an extra parameter to the function and to the optimizer to pass in these extras, which however can only work if the optimizer supports this.

Lexical scoping allows using function closures and maintaining local state. A simple example (taken from Abelson and Sussman) is obtained by typing demo(scoping) at the R prompt. Further information is provided in the standard R reference "R: A Language for Data Analysis and Graphics" (see What documentation exists for R?) and a paper on "Lexical Scope and Statistical Computing" by Robert Gentleman and Ross Ihaka which can be obtained from the doc/misc directory of a CRAN site and will appear in the Journal of Computational and Graphical Statistics around the beginning of 2000.

Lexical scoping also implies a further major difference. Whereas S stores all objects as separate files in a directory somewhere (usually .Data under the current directory), R does not. All objects in R are stored internally. When R is started up it grabs a very large piece of memory and uses it to store the objects. R performs its own memory management of this piece of memory. Having everything in memory is necessary because it is not really possible to externally maintain all relevant "environments" of symbol/value pairs. This difference also seems to make R faster than S.

The down side is that if R crashes you will lose all the work for the current session. Saving and restoring the memory "images" (the functions and data stored in R's internal memory at any time) can be a bit slow, especially if they are big. In S this does not happen, because everything is saved in disk files and if you crash nothing is likely to happen to them. (In fact, one might conjecture that the S developers felt that the price of changing their approach to persistent storage just to accommodate lexical scope was far too expensive.) R is still in a beta stage, and may crash from time to time. Hence, for important work you should consider saving often (see How can I save my workspace?). Other possibilities are logging your sessions, or have your R commands stored in text files which can be read in using source().

Note: If you run R from within Emacs (see R and Emacs), you can save the contents of the interaction buffer to a file and conveniently manipulate it using ess-transcript-mode, as well as save source copies of all functions and data used.


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3.3.2 Models

There are some differences in the modeling code, such as


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3.3.3 Others

Apart from lexical scoping and its implications, R follows the S language definition in the Blue Book as much as possible, and hence really is an "implementation" of S. There are some intentional differences where the behavior of S is considered "not clean". In general, the rationale is that R should help you detect programming errors, while at the same time being as compatible as possible with S.

Some known differences are the following.

There are also differences which are not intentional, and result from missing or incorrect code in R. The developers would appreciate hearing about any deficiencies you may find (in a written report fully documenting the difference as you see it). Of course, it would be useful if you were to implement the change yourself and make sure it works.


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3.4 Is there anything R can do that S-PLUS cannot?

Since almost anything you can do in R has source code that you could port to S-PLUS with little effort there will never be much you can do in R that you couldn't do in S-PLUS if you wanted to. (Note that using lexical scoping may simplify matters considerably, though.)

R offers several graphics features that S-PLUS does not, such as finer handling of line types, more convenient color handling (via palettes), gamma correction for color, and, most importantly, mathematical annotation in plot texts, via input expressions reminiscent of TeX constructs. Unfortunately, this feature still is mostly undocumented. The paper "An Approach to Providing Mathematical Annotation in Plots" by Paul Murrell and Ross Ihaka, which will soon appear in the Journal of Computational and Graphical Statistics, has more details on this.


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4 R Web Interfaces

Rcgi is a CGI WWW interface to R by Mark J Ray. Recent version have the ability to use "embedded code": you can mix user input and code, allowing the HTML author to do anything from load in data sets to enter most of the commands for users without writing CGI scripts. Graphical output is possible in PostScript or GIF formats and the executed code is presented to the user for revision.

Demo and download are available from http://www.mth.uea.ac.uk/~h089/Rcgi/.

Rweb is developed and maintained by Jeff Banfield. The Rweb Home Page provides access to all three versions of Rweb--a simple text entry form that returns output and graphs, a more sophisticated Javascript version that provides a multiple window environment, and a set of point and click modules that are useful for introductory statistics courses and require no knowledge of the R language. All of the Rweb versions can analyze Web accessible datasets if a URL is provided.

A paper on Rweb, providing a detailed explanation of the different versions of Rweb and an overview of how Rweb works, was published in the Journal of Statistical Software (http://www.stat.ucla.edu/journals/jss/).


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5 R Add-On Packages


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5.1 Which add-on packages exist for R?

The R distribution comes with the following extra packages:

eda
Exploratory Data Analysis. Currently only contains functions for robust line fitting, and median polish and smoothing.
lqs
Resistant regression and covariance estimation.
modreg
MODern REGression: smoothing and local methods.
mva
MultiVariate Analysis. Currently contains code for principal components, canonical correlations, metric multidimensional scaling, and hierarchical and k-means clustering.
nls
Nonlinear regression routines.
splines
Regression spline functions and classes.
stepfun
Code for dealing with step functions, including empirical cumulative distribution functions.
ts
Time series.

The following packages are available from the CRAN src/contrib area.

KernSmooth
Functions for kernel smoothing (and density estimation) corresponding to the book "Kernel Smoothing" by M. P. Wand and M. C. Jones, 1995.
MASS
Functions and datasets from the main library of Venables and Ripley, "Modern Applied Statistics with S-PLUS". Contained in VR.
NISTnls
A set of test nonlinear least squares examples from NIST, the U.S. National Institute for Standards and Technology.
RmSQL
An interface between R and the mSQL database system.
Rnotes
The data sets for the exercises in Rnotes (see What documentation exists for R?).
acepack
ace (Alternating Conditional Expectations) and avas (Additivity and VAriance Stabilization for regression) for selecting regression transformations.
akima
Linear or cubic spline interpolation for irregularly gridded data.
ash
Programs for 1D and 2D density estimation.
bindata
Generation of correlated artificial binary data.
boot
Functions and datasets for bootstrapping from the book "Bootstrap Methods and Their Applications" by A. C. Davison and D. V. Hinkley, 1997, Cambridge University Press.
bootstrap
Software (bootstrap, cross-validation, jackknife), data and errata for the book "An Introduction to the Bootstrap" by B. Efron and R. Tibshirani, 1993, Chapman and Hall.
cclust
Convex clustering methods, including k-means algorithm, on-line update algorithm (Hard Competitive Learning) and Neural Gas algorithm (Soft Competitive Learning) and calculation of several indexes for finding the number of clusters in a data set.
chron
A package for working with chronological objects (times and dates).
class
Functions for classification (k-nearest neighbor and LVQ). Contained in VR.
cluster
Functions for cluster analysis.
coda
Output analysis and diagnostics for Markov Chain Monte Carlo (MCMC) simulations.
ctest
A collection of classical tests, including the Bartlett, Fisher, Kruskal-Wallis, Kolmogorov-Smirnov, and Wilcoxon tests.
date
Functions for dealing with dates. The most useful of them accepts a vector of input dates in any of the forms 8/30/53, 30Aug53, 30 August 1953, ..., August 30 53, or any mixture of these.
e1071
Miscellaneous functions used at the Department of Statistics at TU Wien (E1071).
fracdiff
Maximum likelihood estimation of the parameters of a fractionally differenced ARIMA(p,d,q) model (Haslett and Raftery, Applied Statistics, 1989).
funfits
An integrated set of functions for fitting curves and surfaces including thin plate splines, kriging and neural networks.
gee
An implementation of the Liang/Zeger generalized estimating equation approach to GLMs for dependent data.
gss
A comprehensive package for structural multivariate function estimation using smoothing splines.
integrate
Adaptive quadrature in up to 20 dimensions.
leaps
A package which performs an exhaustive search for the best subsets of a given set of potential regressors, using a branch-and-bound algorithm, and also performs searches using a number of less time-consuming techniques.
lmtest
A collection of tests on the assumptions of linear regression models from the book "The linear regression model under test" by W. Kraemer and H. Sonnberger, 1986, Physica.
locfit
Local Regression, likelihood and density estimation.
logspline
Logspline density estimation.
mclust
Model-based cluster analysis.
mda
Code for mixture discriminant analysis (MDA), flexible discriminant analysis (FDA), penalized discriminant analysis (PDA), multivariate additive regression splines (MARS), adaptive back-fitting splines (BRUTO), and penalized regression.
mlbench
A collection of artificial and real-world machine learning benchmark problems, including the Boston housing data.
multilm
A basic method for fitting and testing multivariate linear models, including stabilized test procedures by Laeuter et. al.
multiv
Functions for hierarchical clustering, partitioning, bond energy algorithm, Sammon mapping, PCA and correspondence analysis.
nlme
Fit and compare Gaussian linear and nonlinear mixed-effects models.
nnet
Software for single hidden layer perceptrons ("feed-forward neural networks"), and for multinomial log-linear models. Contained in VR.
norm
Analysis of multivariate normal datasets with missing values.
oz
Functions for plotting Australia's coastline and state boundaries.
pls
Univariate Partial Least Squares Regression.
polymars
Polychotomous regression based on Multivariate Adaptive Regression Splines.
polynom
A collection of functions to implement a class for univariate polynomial manipulations.
princurve
Fits a principal curve to a matrix of points in arbitrary dimension.
pspline
Smoothing splines with penalties on order m derivatives.
quadprog
For solving quadratic programming problems.
quantreg
Compute regression quantiles and some related rank statistics.
rmeta
Functions for simple fixed and random effects meta-analysis for two-sample comparison of binary outcomes.
rpart
Recursive Partitioning.
sgeostat
An object-oriented framework for geostatistical modeling.
sm
Software linked to the book "Applied Smoothing Techniques for Data Analysis: The Kernel Approach with S-PLUS Illustrations" by A. W. Bowman and A. Azzalini (1997), Oxford University Press.
spatial
Functions for kriging and point pattern analysis from "Modern Applied Statistics with S-PLUS" by W. Venables and B. Ripley. Contained in VR.
stable
Density, distribution, quantile and hazard functions of a stable variate; generalized linear models for the parameters of a stable distribution.
stataread
Read and write Stata v6 .dta files.
survival5
Functions for survival analysis, version 5 (requires splines and suggests date), the main new feature being penalised (partial) likelihood.
tree
Classification and regression trees.
tripack
A constrained two-dimensional Delaunay triangulation package.
tseries
Additional code for time series analysis.
wavethresh
Software to perform 1-d and 2-d wavelet statistics and transforms.
xgobi
Interface to the XGobi and XGvis programs for graphical data analysis.

See CRAN src/contrib/INDEX for more information.

There is also a CRAN src/contrib/Devel directory which contains packages still "under development" or depending on features only present in the current development versions of R. Volunteers are invited to give these a try, of course. This area of CRAN currently contains

bats
Basic time series modelling functions.
dopt
Finding D-optimal experimental designs.
tcltk
Basic interface with Tcl/Tk.
timeslab
Time series routines.
vtcl
Interface to Visual Tcl.
Jim Lindsey has written a collection of R packages for nonlinear regression and repeated measurements, consisting of event (procedures for event history analysis), gnlm (generalized nonlinear regression models), growth (normal theory repeated measurements models), repeated (models for non-normal repeated measurements.), and rmutil (tools for repeated measurements). Jim's packages were used for all analyses in the new edition of his book "Models for Repeated Measurements" (1999, Oxford University Press), and can be obtained from http://www.luc.ac.be/~jlindsey/rcode.html. Paul Gilbert has written the Dynamic Systems Estimation (DSE) Library, a multivariate time series package which implements an object oriented approach to time series models (using classes and methods in R/S). The package provides state-space models and the Kalman filter, VARMA and cointegration models, and numerical differentiation. It also contains Troll models as another class (the Troll interface is not yet functional in R). Paul's package dse can be obtained via http://www.bank-banque-canada.ca/pgilbert/dsedesc.htm.

More code has been posted to the r-help mailing list, and can be obtained from the mailing list archive.


Node:How can add-on packages be installed?, Next:, Previous:Which add-on packages exist for R?, Up:R Add-On Packages

5.2 How can add-on packages be installed?

(Unix only.) The add-on packages on CRAN come as gzipped tar files (which may contain more than one package). First "unpack" the files of interest. If you have GNU tar, you can use tar zxf name, otherwise you can use gunzip -c name | tar xf -.

Let pkgdir_1, ..., pkgdir_n be the (relative or absolute) path names of the packages to be installed. (In the simplest case, the unpacking creates a single package directory, and its name is used.) To install to the default R directory tree (the library subdirectory of R_HOME), type

$ R INSTALL pkgdir_1 ... pkgdir_n

at the shell prompt. To install to another tree (e.g., your private one), use

$ R INSTALL -l lib pkgdir_1 ... pkgdir_n

where lib gives the path to the library tree to install to.

As of R version 0.65.1, you no longer need to explicitly unpack for installing; i.e., you can do R INSTALL /path/to/pkg_ver.tar.gz.

You can use several library trees of add-on packages. The easiest way to tell R to use these is via the environment variable R_LIBS which should be a colon-separated list of directories at which R library trees are rooted. You do not have to specify the default tree in R_LIBS. E.g., to use a private tree in $HOME/lib/R and a public site-wide tree in /usr/local/lib/R/site, put

R_LIBS="$HOME/lib/R:/usr/local/lib/R/site"; export R_LIBS

into your (Bourne) shell profile or your ~/.Renviron file.


Node:How can add-on packages be used?, Next:, Previous:How can add-on packages be installed?, Up:R Add-On Packages

5.3 How can add-on packages be used?

To find out which additional packages are available on your system, type

library()

at the R prompt.

This produces something like

Packages in `/home/me/lib/R':

mystuff      My own R functions, nicely packaged but not documented

Packages in `/usr/local/lib/R/library':

MASS         Main package of Venables and Ripley's MASS
base         The R base package
class        Functions for classification
cluster      Functions for clustering
ctest        Classical tests
date         Functions for handling dates
eda          Exploratory Data Analysis
gee          Generalized Estimating Equation models
lme          Linear mixed effects library
locfit       Local regression, likelihood and density estimation
lqs          Resistant regression and covariance estimation
modreg       Modern regression: smoothing and local methods
mva          Classical Multivariate Analysis
nls          Nonlinear regression
nnet         Software for feed-forward neural networks with a single
             hidden layer and for multinomial log-linear models.
splines      Regression spline functions and classes
stepfun      Step functions, including empirical distributions
survival5    Survival analysis
ts           Time series functions

You can "load" the installed package pkg by

library(pkg)

You can then find out which functions it provides by typing one of

help(package = pkg)
library(help = pkg)

You can unload the loaded package pkg by

detach("package:pkg")


Node:How can add-on packages be removed?, Next:, Previous:How can add-on packages be used?, Up:R Add-On Packages

5.4 How can add-on packages be removed?

To remove the packages pkg_1, ..., pkg_n from the default library or the library lib, do

$ R REMOVE pkg_1 ... pkg_n

or

$ R REMOVE -l lib pkg_1 ... pkg_n

respectively.


Node:How can I create an R package?, Next:, Previous:How can add-on packages be removed?, Up:R Add-On Packages

5.5 How can I create an R package?

A package consists of a subdirectory containing the files DESCRIPTION, INDEX, and TITLE, and the subdirectories R, data, exec, inst, man and src (some of which can be missing).

The DESCRIPTION file contains basic information about the package in the following format:

Package: e1071
Version: 0.7-3
Author: Compiled by Fritz Leisch <Friedrich.Leisch@ci.tuwien.ac.at>.
Description: Miscellaneous functions used at the Department of
        Statistics at TU Wien (E1071).
Depends:
License: GPL version 2 or later

The license field should contain an explicit statement or a well-known abbreviation (such as GPL, LGPL, BSD and Artistic), maybe followed by a reference to the actual license file. It is very important that you include this information! Otherwise, it may not even be legally correct for others to distribute copies of the package.

The TITLE file contains a line giving the name of the package and a brief description. INDEX contains a line for each sufficiently interesting object in the package, giving its name and a description (functions such as print methods not usually called explicitly might not be included). Note that you can automatically create this file using something like R CMD Rdindex man/*.Rd > INDEX provided that Perl is available on your system.

The R subdirectory contains code files. The code files to be installed must start with a (lower- or uppercase) letter and have one of the extensions .R, .S, .q, .r, or .s. We recommend using .R, as this extension seems to be not used by any other software. It should be possible to read in the files using source(), so R objects must be created by assignments. Note that there has to be no connection between the name of the file and the R objects created by it. If necessary, one of these files (historically zzz.R) should use library.dynam() inside .First.lib() to load compiled code.

The man subdirectory should contain documentation files for the objects in the package. The documentation files to be installed must also start with a (lower- or uppercase) letter and have the extension .Rd (the default) or .rd.

C or FORTRAN source and optionally a Makefile for the compiled code is in src. Note that the Makefile most likely is not needed.

The data subdirectory is for additional data files the package makes available for loading using data(). Currently, data files can have one of three types as indicated by their extension: plain R code (.R or .r), tables (.tab, .txt, or .csv), or save() images (.RData or .rda). The subdirectory should contain a 00Index file that describes the datasets available.

The contents of the inst subdirectory will be copied recursively to the installation directory.

Finally, exec could contain additional executables the package needs, typically Shell or Perl scripts. This mechanism is currently not used by any package, and still experimental.

You can also provide (Bourne) shell scripts configure and cleanup for configuration before installation (such as checking for additional software that might be needed by the package), and removing the files created in this process. See the add-on package e1071 on CRAN for an example of this mechanism.

See the documentation for library() for more information.

The web page http://www.biostat.washington.edu/~thomas/Rlib.html maintained by Thomas Lumley provides information on porting S packages to R.

See What is CRAN?, for information on uploading a package to CRAN.


Node:How can I contribute to R?, Previous:How can I create an R package?, Up:R Add-On Packages

5.6 How can I contribute to R?

R is in active development and there is always a risk of bugs creeping in. Also, the developers do not have access to all possible machines capable of running R. So, simply using it and communicating problems is certainly of great value.

One place where functionality is still missing is the modeling software as described in "Statistical Models in S" (see What is S?); Generalized Additive Models (gam) and some of the nonlinear modeling code are not there yet.

See also the PROJECTS file in the top level R source directory.

Many (more) of the packages available at the Statlib S Repository might be worth porting to R.

If you are interested in working on any of these projects, please notify Kurt Hornik.


Node:R and Emacs, Next:, Previous:R Add-On Packages, Up:Top

6 R and Emacs


Node:Is there Emacs support for R?, Next:, Previous:R and Emacs, Up:R and Emacs

6.1 Is there Emacs support for R?

There is an Emacs package which provides a standard interface between statistical programs and statistical processes called ESS ("Emacs Speaks Statistics"). It is intended to provide assistance for interactive statistical programming and data analysis. Languages supported include: S dialects (S 3/4, S-PLUS 3.x/4.x/5.x, and R), LispStat dialects (XLispStat, ViSta), SAS, Stata, SPSS dialects (SPSS, Fiasco) and SCA.

ESS grew out of the desire for bug fixes and extensions to S-mode 4.8 (which was a GNU Emacs interface to S/S-PLUS version 3 only). The current set of developers desired support for XEmacs, R, S4, and MS Windows. In addition, with new modes being developed for R, Stata, and SAS, it was felt a unifying interface and framework for the user interface, would benefit both the user and the developer, by helping both groups conform to standard Emacs usage. The end result is an increase in efficiency for statistical programming and data analysis, over the usual tools.

R support contains code for editing R source code (syntactic indentation and highlighting of source code, partial evaluations of code, loading and error-checking of code, and source code revision maintenance) and documentation (syntactic indentation and highlighting of source code, sending Examples to running ESS process, and previewing), interacting with an inferior R process from within Emacs (command-line editing, searchable command history, command-line completion of R object and file names, quick access to object and search lists, transcript recording, and an interface to the help system), and transcript manipulation (recording and saving transcript files, manipulating and editing saved transcripts, and re-evaluating commands from transcript files).

The latest versions of ESS are available from http://ess.stat.wisc.edu/pub/ESS/ or ftp://ess.stat.wisc.edu/pub/ESS/, or via CRAN. The HTML version of the documentation can be found at http://stat.ethz.ch/ESS/.

ESS comes with detailed installation instructions.

For help with ESS, send email to ESS-help@stat.ethz.ch.

Please send bug reports and suggestions on ESS to ESS-bugs@stat.math.ethz.ch. The easiest way to do this from is within Emacs by typing M-x ess-submit-bug-report or using the [ESS] or [iESS] pulldown menus.


Node:Should I run R from within Emacs?, Previous:Is there Emacs support for R?, Up:R and Emacs

6.2 Should I run R from within Emacs?

Yes, definitely. Inferior R mode provides a readline/history mechanism, object name completion, and syntax-based highlighting of the interaction buffer using Font Lock mode, as well as a very convenient interface to the R help system.

Of course, it also integrates nicely with the mechanisms for editing R source using Emacs. One can write code in one Emacs buffer and send whole or parts of it for execution to R; this is helpful for both data analysis and programming. One can also seamlessly integrate with a revision control system, in order to maintain a log of changes in your programs and data, as well as to allow for the retrieval of past versions of the code.

In addition, it allows you to keep a record of your session, which can also be used for error recovery through the use of the transcript mode.

To specify command line arguments for the inferior R process, use C-u M-x R for starting R. This prompts you for the arguments; in particular, you can increase the memory size this way (see Why does R run out of memory?).


Node:R Miscellania, Next:, Previous:R and Emacs, Up:Top

7 R Miscellania


Node:Why does R run out of memory?, Next:, Previous:R Miscellania, Up:R Miscellania

7.1 Why does R run out of memory?

R (currently) uses a static memory model. This means that when it starts up, it asks the operating system to reserve a fixed amount of memory for it. The size of this chunk cannot be changed subsequently. Hence, it can happen that not enough memory was allocated, e.g., when trying to read large data sets into R.

In these cases, you should restart R with more memory available, using the command line options --nsize and --vsize. To understand these options, one needs to know that R maintains separate areas for fixed and variable sized objects. The first of these is allocated as an array of "cons cells" (Lisp programmers will know what they are, others may think of them as the building blocks of the language itself, parse trees, etc.), and the second are thrown on a "heap". The --nsize option can be used to specify the number of cons cells which R is to use (the default is 250000), and the --vsize option to specify the size of the vector heap in bytes (the default is 6 MB). Boths options must either be integers or integers ending with M, K, or k meaning `Mega' (2^20), (computer) `Kilo' (2^10), or regular `kilo' (1000).

E.g., to read in a table of 5000 observations on 40 numeric variables, R --vsize 6M should do (which currently is the default).

Note that the information on where to find vectors and strings on the heap is stored using cons cells. Thus, it may also be necessary to allocate more space for cons cells in order to perform computations with very "large" variable-size objects.

You can find out the current memory consumption (the proportion of heap and cons cells used) by typing gc() at the R prompt. This may help you in finding out whether to increase --vsize or --nsize. Note that following gcinfo(TRUE), automatic garbage collection always prints memory use statistics.

As of version 0.62.3, R will tell you whether you ran out of cons or heap memory.

The defaults for --nsize and --vsize can be changed by setting the environment variables R_NSIZE and R_VSIZE respectively, perhaps most conveniently on Unix in the R environment file (~/.Renviron by default).

When using read.table(), the memory requirements are in fact higher than anticipated, because the file is first read in as one long string which is then split again. Use scan() if possible in case you run out of memory when reading in a large table.


Node:Why does sourcing a correct file fail?, Next:, Previous:Why does R run out of memory?, Up:R Miscellania

7.2 Why does sourcing a correct file fail?

R sometimes has problems parsing a file which does not end in a newline. This can happen for example when Emacs is used for editing the file and next-line-add-newlines is set to nil. To avoid the problem, either set require-final-newline to a non-nil value in one of your Emacs startup files, or make sure R-mode (see Is there Emacs support for R?) is used for editing R source files (which locally ensures this setting).

Earlier R versions had a similar problem when reading in data files, but this should have been taken care of now.


Node:How can I set components of a list to NULL?, Next:, Previous:Why does sourcing a correct file fail?, Up:R Miscellania

7.3 How can I set components of a list to NULL?

You can use

x[i] <- list(NULL)

to set component i of the list x to NULL, similarly for named components. Do not set x[i] or x[[i]] to NULL, because this will remove the corresponding component from the list.

For dropping the row names of a matrix x, it may be easier to use rownames(x) <- NULL, similarly for column names.


Node:How can I save my workspace?, Next:, Previous:How can I set components of a list to NULL?, Up:R Miscellania

7.4 How can I save my workspace?

save.image() saves the objects in the user's .GlobalEnv to the file .RData in the R startup directory. (This is also what happens after q("yes").) Using save.image(file) one can save the image under a different name.


Node:How can I clean up my workspace?, Next:, Previous:How can I save my workspace?, Up:R Miscellania

7.5 How can I clean up my workspace?

To remove all objects in the currently active environment (typically .GlobalEnv), you can do

rm(list = ls(all = TRUE))

(Without all = TRUE, only the objects with names not starting with a `.' are removed.)


Node:How can I get eval() and D() to work?, Next:, Previous:How can I clean up my workspace?, Up:R Miscellania

7.6 How can I get eval() and D() to work?

Strange things will happen if you use eval(print(x), envir = e) or D(x^2, "x"). The first one will either tell you that "x" is not found, or print the value of the wrong x. The other one will likely return zero if x exists, and an error otherwise.

This is because in both cases, the first argument is evaluated in the calling environment first. The result (which should be an object of mode `expression' or `call') is then evaluated or differentiated. What you (most likely) really want is obtained by "quoting" the first argument upon surrounding it with expression(). For example,

R> D(expression(x^2), "x")
2 * x

Although this behavior may initially seem to be rather strange, is perfectly logical. The "intuitive" behavior could easily be implemented, but problems would arise whenever the expression is contained in a variable, passed as a parameter, or is the result of a function call. Consider for instance the semantics in cases like

D2 <- function(e, n) D(D(e, n), n)

or

g <- function(y) eval(substitute(y), sys.frame(sys.parent(n = 2)))
g(a * b)

See the help pages for more examples.


Node:Why do my matrices lose dimensions?, Next:, Previous:How can I get eval() and D() to work?, Up:R Miscellania

7.7 Why do my matrices lose dimensions?

When a matrix with a single row or column is created by a subscripting operation, e.g., row <- mat[2, ], it is by default turned into a vector. In a similar way if an array with dimension, say, 2 x 3 x 1 x 4 is created by subscripting it will be coerced into a 2 x 3 x 4 array, losing the unnecessary dimension. After much discussion this has been determined to be a feature.

To prevent this happening, add the option drop = FALSE to the subscripting. For example,

rowmatrix <- mat[2, , drop = FALSE]  # creates a row matrix
colmatrix <- mat[, 2, drop = FALSE]  # creates a column matrix
a <- b[1, 1, 1, drop = FALSE]        # creates a 1 x 1 x 1 array

The drop = FALSE option should be used defensively when programming. For example, the statement

somerows <- mat[index, ]

will return a vector rather than a matrix if index happens to have length 1, causing errors later in the code. It should probably be rewritten as

somerows <- mat[index, , drop = FALSE]


Node:How does autoloading work?, Next:, Previous:Why do my matrices lose dimensions?, Up:R Miscellania

7.8 How does autoloading work?

R has a special environment called .AutoloadEnv. Using autoload(name, pkg), where name and pkg are strings giving the names of an object and the package containing it, stores some information in this environment. When R tries to evaluate name, it loads the corresponding package pkg and reevaluates name in the new package's environment.

Using this mechanism makes R behave as if the package was loaded, but does not occupy memory (yet).

See the help page for autoload() for a very nice example.


Node:How should I set options?, Next:, Previous:How does autoloading work?, Up:R Miscellania

7.9 How should I set options?

The function options() allows setting and examining a variety of global "options" which affect the way in which R computes and displays its results. The variable .Options holds the current values of these options, but should never directly be assigned to unless you want to drive yourself crazy--simply pretend that it is a "read-only" variable.

For example, given

test1 <- function(x = pi, dig = 3) {
  oo <- options(digits = dig); on.exit(options(oo));
  cat(.Options$digits, x, "\n")
}
test2 <- function(x = pi, dig = 3) {
  .Options$digits <- dig
  cat(.Options$digits, x, "\n")
}

we obtain:

R> test1()
3 3.14
R> test2()
3 3.141593

What is really used is the global value of .Options, and using options(OPT = VAL) correctly updates it. Local copies of .Options, either in .GlobalEnv or in a function environment (frame), are just silently disregarded.


Node:How do file names work in Windows?, Next:, Previous:How should I set options?, Up:R Miscellania

7.10 How do file names work in Windows?

As R uses C-style string handling, \ is treated as an escape character, so that for example one can enter a newline as \n. When you really need a \, you have to escape it with another \.

Thus, in filenames use something like "c:\\data\\money.dat". You can also replace \ by / ("c:/data/money.dat").


Node:Why does plotting give a color allocation error?, Next:, Previous:How do file names work in Windows?, Up:R Miscellania

7.11 Why does plotting give a color allocation error?

Sometimes plotting, e.g., when running demo(image), results in "Error: color allocation error". This is an X problem, and only indirectly related to R. It occurs when applications started prior to R have used all the available colors. (How many colors are available depends on the X configuration; sometimes only 256 colors can be used.)

One application which is notorious for "eating" colors is Netscape. If the problem occurs when Netscape is running, try (re)starting it with either the -no-install (to use the default colormap) or the -install (to install a private colormap) option.

You could also set the colortype of X11() to `pseudo.cube' rather than the default `pseudo'. See the help page for X11() for more information.


Node:Is R Y2K-compliant?, Previous:Why does plotting give a color allocation error?, Up:R Miscellania

7.12 Is R Y2K-compliant?

We expect R to be Y2K compliant when compiled and run on a Y2K compliant system. In particular R does not internally represent or manipulate dates as two-digit quantities. However, no guarantee of Y2K compliance is provided for R. R is free software and comes with no warranty whatsover.

R, like any other programming language, can be used to write programs and manipulate data in ways that are not Y2K compliant.


Node:R Programming, Next:, Previous:R Miscellania, Up:Top

8 R Programming


Node:How should I write summary methods?, Next:, Previous:R Programming, Up:R Programming

8.1 How should I write summary methods?

Suppose you want to provide a summary method for class foo. Then summary.foo() should not print anything, but return an object of class summary.foo, and you should write a method print.summary.foo() which nicely prints the summary information and invisibly returns its object. This approach is preferred over having summary.foo() print summary information and return something useful, as sometimes you need to grab something computed by summary() inside a function or similar. In such cases you don't want anything printed.


Node:How can I debug dynamically loaded code?, Next:, Previous:How should I write summary methods?, Up:R Programming

8.2 How can I debug dynamically loaded code?

According to Doug Bates, the secret of symbolic debugging of dynamically loaded code is to

When using GUD mode for debugging from within Emacs, you may find it most convenient to use the directory with your code in it as the current working directory and then make a symbolic link from that directory to the R executable. That way .gdbinit can stay in the directory with the code and be used to set up the environment and the search paths for the source, e.g. as follows:

set env R_HOME /opt/R
set env R_PAPERSIZE letter
set env R_PRINTCMD lpr
dir /opt/R/src/appl
dir /opt/R/src/main
dir /opt/R/src/nmath
dir /opt/R/src/unix


Node:How can I inspect R objects when debugging?, Previous:How can I debug dynamically loaded code?, Up:R Programming

8.3 How can I inspect R objects when debugging?

In the C implementation underlying R, all objects are so-called SEXPs (from Lisp's "S-expressions" which comes from "symbolic expression"), which are pointers to data structures called SEXPRECs. (See the file src/include/Rinternals.h in the R sources for the definition of the SEXPREC type.) For example, let

R> DF <- data.frame(a = 1:3, b = 4:6)

By setting a breakpoint at do_get and typing get("DF") at the R prompt, one can find out the address in memory of DF, e.g.

Value returned is $1 = (SEXPREC *) 0x40583e1c
(gdb) p *$1
$2 = {
  sxpinfo = {type = 19, obj = 1, named = 1, gp = 0,
    mark = 0, debug = 0, trace = 0, = 0},
  attrib = 0x40583e80,
  u = {
    vecsxp = {
      length = 2,
      type = {c = 0x40634700 "0>X@D>X@0>X@", i = 0x40634700,
        f = 0x40634700, z = 0x40634700, s = 0x40634700},
      truelength = 1075851272,
    },
    primsxp = {offset = 2},
    symsxp = {pname = 0x2, value = 0x40634700, internal = 0x40203008},
    listsxp = {carval = 0x2, cdrval = 0x40634700, tagval = 0x40203008},
    envsxp = {frame = 0x2, enclos = 0x40634700},
    closxp = {formals = 0x2, body = 0x40634700, env = 0x40203008},
    promsxp = {value = 0x2, expr = 0x40634700, env = 0x40203008}
  }
}

(Debugger output reformatted for better legibility).

Using PrintValue() one can "inspect" the values of the various elements of the SEXP, e.g.,

(gdb) p PrintValue($1->attrib)
$names
[1] "a" "b"

$row.names
[1] "1" "2" "3"

$class
[1] "data.frame"

$3 = void

(Make sure, however, to use PrintValue() on SEXPs with the `obj' bit turned on only.)

To find out where exactly the corresponding information is stored, one needs to go "deeper":

(gdb) set $a = $1->attrib
(gdb) p $a->u.listsxp.tagval->u.symsxp.pname->u.vecsxp.type.c
$4 = 0x405d40e8 "names"
(gdb) p $a->u.listsxp.carval->u.vecsxp.type.s[1]->u.vecsxp.type.c
$5 = 0x40634378 "b"
(gdb) p $1->u.vecsxp.type.s[0]->u.vecsxp.type.i[0]
$6 = 1
(gdb) p $1->u.vecsxp.type.s[1]->u.vecsxp.type.i[1]
$7 = 5


Node:R Bugs, Next:, Previous:R Programming, Up:Top

9 R Bugs


Node:What is a bug?, Next:, Previous:R Bugs, Up:R Bugs

9.1 What is a bug?

If R executes an illegal instruction, or dies with an operating system error message that indicates a problem in the program (as opposed to something like "disk full"), then it is certainly a bug. If you call .Internal(), .External(), .C() or .Fortran() yourself (or in a function you wrote), you can always crash R by using wrong argument types (modes). This is not a bug.

Taking forever to complete a command can be a bug, but you must make certain that it was really R's fault. Some commands simply take a long time. If the input was such that you know it should have been processed quickly, report a bug. If you don't know whether the command should take a long time, find out by looking in the manual or by asking for assistance.

If a command you are familiar with causes an R error message in a case where its usual definition ought to be reasonable, it is probably a bug. If a command does the wrong thing, that is a bug. But be sure you know for certain what it ought to have done. If you aren't familiar with the command, or don't know for certain how the command is supposed to work, then it might actually be working right. Rather than jumping to conclusions, show the problem to someone who knows for certain.

Finally, a command's intended definition may not be best for statistical analysis. This is a very important sort of problem, but it is also a matter of judgment. Also, it is easy to come to such a conclusion out of ignorance of some of the existing features. It is probably best not to complain about such a problem until you have checked the documentation in the usual ways, feel confident that you understand it, and know for certain that what you want is not available. If you are not sure what the command is supposed to do after a careful reading of the manual this indicates a bug in the manual. The manual's job is to make everything clear. It is just as important to report documentation bugs as program bugs. However, we know that the introductory documentation is seriously inadequate, so you don't need to report this.

If the online argument list of a function disagrees with the manual, one of them must be wrong, so report the bug.


Node:How to report a bug, Previous:What is a bug?, Up:R Bugs

9.2 How to report a bug

When you decide that there is a bug, it is important to report it and to report it in a way which is useful. What is most useful is an exact description of what commands you type, starting with the shell command to run R, until the problem happens. Always include the version of R, machine, and operating system that you are using; type version in R to print this.

The most important principle in reporting a bug is to report facts, not hypotheses or categorizations. It is always easier to report the facts, but people seem to prefer to strain to posit explanations and report them instead. If the explanations are based on guesses about how R is implemented, they will be useless; others will have to try to figure out what the facts must have been to lead to such speculations. Sometimes this is impossible. But in any case, it is unnecessary work for the ones trying to fix the problem.

For example, suppose that on a data set which you know to be quite large the command

R> data.frame(x, y, z, monday, tuesday)

never returns. Do not report that data.frame() fails for large data sets. Perhaps it fails when a variable name is a day of the week. If this is so then when others got your report they would try out the data.frame() command on a large data set, probably with no day of the week variable name, and not see any problem. There is no way in the world that others could guess that they should try a day of the week variable name.

Or perhaps the command fails because the last command you used was a method for "["() that had a bug causing R's internal data structures to be corrupted and making the data.frame() command fail from then on. This is why others need to know what other commands you have typed (or read from your startup file).

It is very useful to try and find simple examples that produce apparently the same bug, and somewhat useful to find simple examples that might be expected to produce the bug but actually do not. If you want to debug the problem and find exactly what caused it, that is wonderful. You should still report the facts as well as any explanations or solutions. Please include an example that reproduces the problem, preferably the simplest one you have found.

Invoking R with the --vanilla option may help in isolating a bug. This ensures that the site profile and saved data files are not read.

On Unix systems a bug report can be generated using the function bug.report(). This automatically includes the version information and sends the bug to the correct address. Alternatively the bug report can be emailed to r-bugs@lists.r-project.org or submitted to the Web page at http://bugs.r-project.org.

Bug reports on contributed packages should perhaps be sent to the package maintainer rather than to r-bugs.


Node:Acknowledgments, Previous:R Bugs, Up:Top

10 Acknowledgments

Of course, many many thanks to Robert and Ross for the R system, and to the package writers and porters for adding to it.

Special thanks go to Doug Bates, Peter Dalgaard, Paul Gilbert, Fritz Leisch, Jim Lindsey, Thomas Lumley, Martin Maechler, Brian D. Ripley, Anthony Rossini, and Andreas Weingessel for their comments which helped me improve this FAQ.

More to some soon ...