Returns a vector or array or list of values obtained by applying a function to margins of an array or matrix.
apply(X, MARGIN, FUN, ...)
- an array, including a matrix.
- a vector giving the subscripts which the function will be applied over. E.g., for a matrix
c(1, 2)indicates rows and columns. Where
Xhas named dimnames, it can be a character vector selecting dimension names.
- the function to be applied: see ‘Details’. In the case of functions like
%*%, etc., the function name must be backquoted or quoted.
- optional arguments to
X is not an array but an object of a class with a non-null
dim value (such as a data frame),
apply attempts to coerce it to an array via
as.matrix if it is two-dimensional (e.g., a data frame) or via
FUN is found by a call to
match.fun and typically is either a function or a symbol (e.g. a backquoted name) or a character string specifying a function to be searched for from the environment of the call to
... cannot have the same name as any of the other arguments, and care may be needed to avoid partial matching to
FUN. In general-purpose code it is good practice to name the first three arguments if
... is passed through: this both avoids partial matching to
FUN and ensures that a sensible error message is given if arguments named
FUN are passed through
If each call to
FUN returns a vector of length
apply returns an array of dimension
c(n, dim(X)[MARGIN]) if
n > 1. If
apply returns a vector if
MARGIN has length 1 and an array of dimension
dim(X)[MARGIN] otherwise. If
In all cases the result is coerced by
as.vector to one of the basic vector types before the dimensions are set, so that (for example) factor results will be coerced to a character array.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
## Compute row and column sums for a matrix: x <- cbind(x1 = 3, x2 = c(4:1, 2:5)) dimnames(x)[] <- letters[1:8] 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))) stopifnot( apply(x, 2, is.vector)) ## Sort the columns of a matrix apply(x, 2, sort) ##- function with extra args: cave <- function(x, c1, c2) c(mean(x[c1]), mean(x[c2])) apply(x, 1, cave, c1 = "x1", c2 = c("x1","x2")) ma <- matrix(c(1:4, 1, 6:8), nrow = 2) ma apply(ma, 1, table) #--> a list of length 2 apply(ma, 1, stats::quantile) # 5 x n matrix with rownames stopifnot(dim(ma) == dim(apply(ma, 1:2, sum))) ## Example with different lengths for each call z <- array(1:24, dim = 2:4) zseq <- apply(z, 1:2, function(x) seq_len(max(x))) zseq ## a 2 x 3 matrix typeof(zseq) ## list dim(zseq) ## 2 3 zseq[1,] apply(z, 3, function(x) seq_len(max(x))) # a list without a dim attribute
Documentation reproduced from R 3.0.1. License: GPL-2.