[R] apply to row and column of matrix

[Jinsong Zhao]

Hi there,

I try to calculate the cumsum of row and column of a matrix as follows.

 > m <- matrix(1:10, ncol = 2)
 > m
      [,1] [,2]
[1,]    1    6
[2,]    2    7
[3,]    3    8
[4,]    4    9
[5,]    5   10
 > apply(m, 1, cumsum)
      [,1] [,2] [,3] [,4] [,5]
[1,]    1    2    3    4    5
[2,]    7    9   11   13   15
 > apply(m, 2, cumsum)
      [,1] [,2]
[1,]    1    6
[2,]    3   13
[3,]    6   21
[4,]   10   30
[5,]   15   40

My question is why the dim of the return value of apply(m, 1, cumsum) is 
not 5x2, but 2x5.

Best,

Jinsong