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Apply Functions Over Array Margins


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.


If each call to 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].

See Also

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)
apply(ma, 1, table)  #--> a list of length 2