Not quite sure if this is what you're after ... but perhaps it will help.

m <- matrix(c(1, 1, -1, -1, 1, -1, -1, -2, 1, 1, 1, 1), byrow=TRUE, ncol=4)
apply(m, 1, function(x) sum(x[x>0]))/dim(m)[2]
apply(m, 1, function(x) sum(x[x<0]))/dim(m)[2]

Jean


On Tue, Jun 11, 2013 at 7:18 AM, felice <felix11_6@gmx.de> wrote:

> hello,
>
> when i use the function rowMeans, which is sum/n, can i divide it in 2
> parts, -> Sum(just positive values)/n and Sum(just negative values)/n. i
> need both for my regression but dont know how to do it.
>
> for example we have the matrix
>
> 1  1  -1  -1   -> rowMeans([1:3 , 2])  just positive -> 1
> 1 -1 -1  -2
> 1/2  here not 0 because we dont use the -1
> 1 1   1   1
> 1
>
>
> thanks for helping
>
>
>
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