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@section XML

@section XML

@cindex XML

@cindex XML

When reading data from text files, it is the responsibility of the user

When reading data from text files, it is the responsibility of the user

to know and to specify the conventions used to create that file,

to know and to specify the conventions used to create that file,

separator, the representation for missing values (and so on) described

separator, the representation for missing values (and so on) described

in @ref{Export to text files}.  A markup language which can be used to

in @ref{Export to text files}.  A markup language which can be used to

describe not only content but also the structure of the content can

describe not only content but also the structure of the content can

make a file self-describing, so that one need not provide these details

make a file self-describing, so that one need not provide these details

to the software reading the data.

to the software reading the data.

Function @code{scan} has many arguments, most of which we have already

Function @code{scan} has many arguments, most of which we have already

covered under @code{read.table}.  The most crucial argument is

covered under @code{read.table}.  The most crucial argument is

@code{what}, which specifies a list of modes of variables to be read

@code{what}, which specifies a list of modes of variables to be read

from the file.  If the list is named, the names are used for the

from the file.  If the list is named, the names are used for the

components of the returned list.  Modes can be numeric, character or

components of the returned list.  Modes can be numeric, character or

@code{""} or @code{0i}.  For example

@code{""} or @code{0i}.  For example

@example

@example

cat("2 3 5 7", "11 13 17 19", file="ex.dat", sep="\n")

cat("2 3 5 7", "11 13 17 19", file="ex.dat", sep="\n")

scan(file="ex.dat", what=list(x=0, y="", z=0), flush=TRUE)

scan(file="ex.dat", what=list(x=0, y="", z=0), flush=TRUE)

@findex seek

@findex seek

@findex isSeekable

@findex isSeekable

The generic function @code{seek} can be used to read and (on some

The generic function @code{seek} can be used to read and (on some

connections) reset the current position for reading or writing.

connections) reset the current position for reading or writing.

Unfortunately it depends on OS facilities which may be unreliable

Unfortunately it depends on OS facilities which may be unreliable

reports if @code{seek} can change the position on the connection

reports if @code{seek} can change the position on the connection

given by its argument.

given by its argument.

@findex truncate

@findex truncate

The function @code{truncate} can be used to truncate a file opened for

The function @code{truncate} can be used to truncate a file opened for

written to the file as a stream of bytes exactly as it is represented in

written to the file as a stream of bytes exactly as it is represented in

memory.

memory.

@code{readBin} reads a stream of bytes from the file and interprets them

@code{readBin} reads a stream of bytes from the file and interprets them

as a vector of mode given by @code{what}.  This can be either an object

as a vector of mode given by @code{what}.  This can be either an object

string describing the mode (one of the five given in the previous

string describing the mode (one of the five given in the previous

paragraph or @code{"double"} or @code{"int"}).  Argument @code{n}

paragraph or @code{"double"} or @code{"int"}).  Argument @code{n}

specifies the maximum number of vector elements to read from the

specifies the maximum number of vector elements to read from the

connection: if fewer are available a shorter vector will be returned.

connection: if fewer are available a shorter vector will be returned.

Argument @code{signed} allows 1-byte and 2-byte integers to be

Argument @code{signed} allows 1-byte and 2-byte integers to be