apply in r

apply in r

mat1 <- matrix(1:12, nrow = 3)
mat1
#      [,1] [,2] [,3] [,4]
# [1,]    1    4    7   10
# [2,]    2    5    8   11
# [3,]    3    6    9   12

apply(X = mat1, MARGIN = 1, FUN = max)
# [1] 10 11 12

c( max(mat1[1, ]), max(mat1[2, ]), max(mat1[3, ]) )
# [1] 10 11 12

apply(X = mat1, MARGIN = 2, FUN = max)
# [1]  3  6  9 12

c( max(mat1[, 1]), max(mat1[, 2]), max(mat1[, 3]), max(mat1[, 4]) )
# [1]  3  6  9 12

udf_add_n <- function(x, n = 0) {
  x + n
}

apply(mat1, 1, udf_add_n, 3)
#      [,1] [,2] [,3]
# [1,]    4    5    6
# [2,]    7    8    9
# [3,]   10   11   12
# [4,]   13   14   15

arr1 <- array(1:24, dim = c(3,4,2))
apply(arr1, 1, max)
# [1] 22 23 24
apply(arr1, 2, max)
# [1] 15 18 21 24
apply(arr1, 3, max)
# [1] 12 24

.EOF.