| Extract {base} | R Documentation |
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.
x[i]
x[i,j, ...]
x[i,j, ... , drop=TRUE]
x[[i]]
x[[i,j, ...]]
x$name
list, array, matrix.
x <- 1:12; m <- matrix(1:6,nr=2); li <- list(pi=pi, e = exp(1))
x[10] # the tenth element of x
m[1,] # the first row of matrix m
m[1, , drop = FALSE]# is a 1-row matrix
li[[1]] # the first element of list li
y<-list(1,2,a=4,5)
y[c(3,4)] # a list containing the third and fourth elements of y
y$a #the element of y named a