[R] Summing over specific columns in a matrix
emj83
stp08emj at shef.ac.uk
Fri Jan 7 17:29:03 CET 2011
Hi,
I would like to sum some specific columns in my matrix- for example, my
matrix looks like this:
[,1] [,2] [,3] [,4] [,5]
[1,] 1 NA NA NA NA
[2,] 2 1 NA 1 NA
[3,] 3 2 1 2 1
[4,] 4 3 2 3 2
[5,] NA NA NA 4 3
[6,] NA NA NA 5 NA
I would like to find the sum of the first two columns, the second two
columns and the last column:
i.e I am left with a vector of c(16, 18, 6).
I know about colSums and sum overall- I just wondered if this type of
grouping can be included somehow in a vector such as c(2,2,1)? I don't
really want to have to use a loop for this.
Many thanks Emma
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