apply(x, MARGIN, FUN, ...)
x
| the array to be used. |
MARGIN
|
a vector giving the subscripts which the function will
be applied over.
1 indicates rows, 2 indicates columns,
c(1,2) indicates rows and columns.
|
FUN
|
the function to be applied.
In the case of functions like +, %*%, etc., the
function name must be quoted.
|
...
|
optional arguments to FUN.
|
FUN returns a vector of length n, then
apply returns an array of dimension c(n,dim(x)[MARGIN])
if n > 1. If n equals 1, apply returns a
vector if MARGIN has length 1 and an array of dimension
dim(x)[MARGIN] otherwise.
If the calls to FUN return vectors of different lengths,
apply returns a list of length dim(x)[MARGIN].
lapply, tapply, sweep.## Compute row and column sums for a matrix: x <- cbind(x1 = 3, x2 = c(4:1, 2:5)) apply(x, 2, mean, trim = .2) col.sums <- apply(x, 2, sum) row.sums <- apply(x, 1, sum) rbind(cbind(x, Rtot = row.sums), Ctot = c(col.sums, sum(col.sums))) ## Sort the columns of a matrix apply(x, 2, sort) ma <- matrix(c(1:4, 1, 6:8), nr = 2) ma apply(ma, 1, table) #--> a list of length 2