[R] another matrix question

[Rolf Turner]

On 21/04/2008, at 10:05 PM, William Simpson wrote:

> Hi everyone,
>
> I would like to do the following.
>
> Given matrix m and matrix n, I would like to compute mn[i,,j]= m[i,,j]
> + n[i,,j] if either of these elements is 0. (In other words, whichever
> number is nonzero.)
> Else I want mn[i,,j]=(m[i,,j] + n[i,,j])/2
> I need a fast method.

I don't know what you're doing with those double commas --- if m and
n are indeed matrices they make no sense --- but if they should actually
be just commas then what you want is

	mn <- ifelse(m==0 | n==0,m+n,(m+n)/2)
	cheers,

		Rolf Turner

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