Row sums of matrix over/under diagonal

Question

I want to calculate row/col sums for upper/lower triangle matrix (with diagonal). Example:

m <- matrix(1:9, nrow=3)
#result:
upperRowSums(m)
## [1] 12 13 9
lowerRowSums(m)
## [1] 1 7 18

I know that this could be done with simple for loop, but I want to avoid this. I'm looking for pure R solution.

score 4 · Accepted Answer · edited Jul 03 '14 at 21:51

4

A way:

rowSums(m * upper.tri(m, diag=TRUE))
#[1] 12 13  9

edited Jul 03 '14 at 21:51

bartektartanus

answered Jun 29 '14 at 21:03

alexis_laz

5

For those not sure what the `T` references, in expanded form this is: `rowSums(m * upper.tri(m,diag=TRUE))` – thelatemail Jun 29 '14 at 22:15

1 Answers1