[R] array indexing and which

[Werner Wernersen]

Hi R friends!

I am stuck with a stupid question: I can circumvent it
but I would like to 
understand why it is wrong. It would be nice if you
could give me a hint...

I have an 2D array d and do the following:
ids <- which(d[,1]>0)

then I have a vector gk with same column size as d and
do:
ids2 <- which(gk[ids]==1)

but I can't interprete the result I get in ids2.

I get the expected result when I use:
which(gk==1 & d[,1]>0)

Why is the first version wrong?

The reason why I try to use the ids vectors is that I
want to avoid recomputation.

Thanks for your help!
   Werner