Bug in rowCollapse if combined with row subsetting

[const-ae]

Hi Henrik,

I think I found a bug in rowCollapse if it is combined with row subsetting:

mat <- matrix(1:15, nrow = 5, ncol = 3)
print(mat)
#>      [,1] [,2] [,3]
#> [1,]    1    6   11
#> [2,]    2    7   12
#> [3,]    3    8   13
#> [4,]    4    9   14
#> [5,]    5   10   15
matrixStats::rowCollapse(mat, idxs = 2)
#> [1]  6  7  8  9 10
matrixStats::rowCollapse(mat, idxs = 2, rows = 1:4)
#> [1]  6 NA NA NA
matrixStats::rowCollapse(mat, idxs = rep(2, 5), rows = 1:4)
#> [1] 6 7 8 9

^{Created on 2020-03-19 by the reprex package (v0.3.0)} I would expect the last two lines to do the same.

I think the problem is here where the idxs vector is subset. This works well if idxs has nrow(mat) elements, but returns NA if rows is longer than idxs.

If you want, I can draft a quick PR to fix the issue.

[HenrikBengtsson]

Thxs. Fixed for next release.

[HenrikBengtsson]

BTW, this is a good example where full-coverage unit tests != solid system tests. Forgot to test the combination of idxs and subsetting.