The R Project SVN R

\name{Extract}
\title{Extract or Replace Parts of an Object}
\usage{
x[i]
x[i,j, ...]
x[i,j, ... , drop=TRUE]
x[[i]]
x[[i,j, ...]]
x$name
}
\alias{Extract}
\alias{Subscript}
\alias{[}
\alias{[[}
\alias{$}
\description{
These operators act on vectors, matrices, dataframes and lists.
If one of these expressions is on the left hand side of an assignment
then that part of \code{x} is set to the value of the right hand side
of the assignment.

These operators are generic. You can write methods to handle subsetting
of specific classes of data.

The \code{[[} operator requires all relavent subscripts be supplied.
With  the \code{[} operator a comma separated blank indicates that all
entries in that dimension are selected.

When operating on a list the  \code{[[} operator gives the specified
element of the list while the \code{[} operator returns a list with
the specified element(s) in it.
}
\seealso{
\code{\link{list}}, \code{\link{array}}, \code{\link{matrix}}.
}
\examples{
x <- 1:12; m <- matrix(1:6,nr=2); li <- list(pi=pi, e = exp(1))
x[10]   # the tenth element of x
m[1,]   # the first row of matrix m
m[1, , drop = FALSE]# is a 1-row matrix
li[[1]] # the first element of list li
y<-list(1,2,a=4,5)
y[c(3,4)] # a list containing the third and fourth elements of y
y$a      #the element of y named a
}
\keyword{array}
\keyword{list}