Cumulative sum in a matrix

Question

I have a matrix like

A= [ 1 2 4
     2 3 1
     3 1 2 ]

and I would like to calculate its cumulative sum by row and by column, that is, I w

Answer 1

Here is a more efficient implementation using the matrixStats package and a larger example matrix:

library(matrixStats)
A <- matrix(runif(10000*10000, 1, 500), 10000)

# Thilo's answer
system.time(B <- t(apply(apply(A, 2, cumsum), 1, cumsum)))
user  system elapsed 
3.684   0.504   4.201

# using matrixStats
system.time(C <- colCumsums(rowCumsums(A)))
user  system elapsed 
0.164   0.068   0.233 

all.equal(B, C)
[1] TRUE