[R] strange use of sapply

[markleeds at verizon.net]

I've tried and give up. I have a matrix of say 200 columns and 400 rows.

For each odd ( or even i suppose if i wanted to )column, 
I want to know the number of rows in which the value is greater than zero.

So, I did sapply(tempMatrix,2,function(x) sum( x > 0 ))

this almost works but i don't know how to tell
it to only do the odd columns. my guess is , like everything else
in R, this is possible. Thanks.