Combinations of vectors (1 x n) taken m at a time from a matrix (k x n)

Question

I'm new on this forum. I work in R.

I have a matrix (kxn) and I have to considere all combinations of the rows vectors (1 xn) taken 2, 3, 4 at a time.

Example:

Consider a matrix m = diag(c(rep(1, 3))) ,

I want the combinations of the three rows vectors (1 xn) taken 2 at a time:

first: (1,0,0) and (0,1,0)
second: (1,0,0) and (0,0,1)
third: (0,1,0) and (0,0,1)

In a second moment, for each couple, I need to compute the sum on the columns. Any suggestion?

Thanks!

Answer 1

m <- diag(c(rep(1, 3)))
tmp <- combn(nrow(m), 2)
array(t(m[tmp,]), c(ncol(m), 2, ncol(tmp))) 

#, , 1
#
#     [,1] [,2]
#[1,]    1    0
#[2,]    0    1
#[3,]    0    0
#
#, , 2
#
#     [,1] [,2]
#[1,]    1    0
#[2,]    0    0
#[3,]    0    1
#
#, , 3
#
#     [,1] [,2]
#[1,]    0    0
#[2,]    1    0
#[3,]    0    1