R: applying function over matrix and keeping matrix dimensions

Question

So I want to apply a function over a matrix in R. This works really intuitively for simple functions:

> (function(x)x*x)(matrix(1:10, nrow=2))
 [,1] [,2] [,3]         


        

Answer 1

One way is to use apply on both rows and columns:

apply(m,1:2,y)
     [,1] [,2] [,3] [,4] [,5]
[1,]    2   NA    6    8   NA
[2,]    3    5   NA    9   11

You can also do it with subscripting because == is already vectorized:

m[m %% 3 == 0] <- NA
m <- m+1
m
     [,1] [,2] [,3] [,4] [,5]
[1,]    2   NA    6    8   NA
[2,]    3    5   NA    9   11