Extract {base} | R Documentation |
Extract or Replace Parts of an Object
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 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 [[
operator requires all relavent subscripts be supplied.
With the [
operator a comma separated blank indicates that all
entries in that dimension are selected.
When operating on a list the [[
operator gives the specified
element of the list while the [
operator returns a list with
the specified element(s) in it.
Usage
x[i]
x[i,j, ...]
x[i,j, ... , drop=TRUE]
x[[i]]
x[[i,j, ...]]
x$name
See Also
list
, array
, matrix
.
Examples
x <- 1:12; m <- matrix(1:6,nr=2); li <- list(pi=pi, e = exp(1))
x[10] # the tenth element of x
m[1,] # the first row of matrix m
m[1, , drop = FALSE]# is a 1-row matrix
li[[1]] # the first element of list li
y<-list(1,2,a=4,5)
y[c(3,4)] # a list containing the third and fourth elements of y
y$a #the element of y named a