Create a binary matrix under certain conditions

Question

I am trying to create a function that given m and p returns a matrix with m rows and mxp columns. The matrix should have 0's except for p positions, starting at p (number of row).

For example, given m=4 and p=2, the matrix should look like:

1    1    0    0    0    0    0    0
0    0    1    1    0    0    0    0
0    0    0    0    1    1    0    0
0    0    0    0    0    0    1    1

I want to work with big matrices. I know how to do this with loops in other programming languages such as python, but I am sure that it should be an easier and more elegant way to do this in R. I have been playing for a while with diag() without finding the solution.

Answer 1

apply()ing the rep() function to each row (or column, it's the same) of the diagonal matrix:

t(apply(diag(m), 2, rep, each = p))

#      [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8]
# [1,]    1    1    0    0    0    0    0    0
# [2,]    0    0    1    1    0    0    0    0
# [3,]    0    0    0    0    1    1    0    0
# [4,]    0    0    0    0    0    0    1    1