On 18-08-2012, at 05:28, Yingwei Lee wrote:
> Hi all,
> I'm just having trouble getting row means of a matrix which
> contain zero.
> For example.
>
> m=matrix(c(1:4, c(0, 0, 0, 0), c(1, 0, 1, 1)), nc=4, byrow=TRUE)
>
> I want to be able to calculate means for non-zero elements for each row.
>
> ## what i have is this
> apply((m[apply(m != 0, MARGIN=1, any),]), 1, mean)
> ## which returns
> [1] 2.50 0.75
>
> ### what i want to get returned is this
> [1] 2.50 *1
>
> *meaning that the last row calculated the mean ignoring the zero. Anyone
> got any ideas?
Define function to compute mean of non zero elements
f <- function(x) {k <- which(x!=0); mean(x[k])}
then use apply
apply(A,1,f)
[1] 2.5 NaN 1.0
and to remove the NaN you could do
z <- apply(A,1,f)
z[!is.na(z)]
or
z[is.finite(z)]
Berend
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