[R] 0 * NA = NA

[Liaw, Andy]

From: Alberto Monteiro
> 
> Is there any way to "force" 0 * NA to be 0 instead of NA?
> 
> For example, suppose I have a vector with some valid values, 
> while other values are NA. If I matrix-pre-multiply this by a 
> weight row vector, whose weights that correspond to the NAs 
> are zero, the outcome will still be NA:
> 
> x <- c(1, NA, 1)
> wt <- c(2, 0, 1)
> wt %*% x # NA

I don't think it's prudent to bend arthmetic rules of a system,
especially when there are good reasons for them.  Here's one:

R> 0 * Inf
[1] NaN

If you are absolutely sure that the Nas in x cannot be Inf (or -Inf),
you might try to force the result to 0, but the only way I can think of
is to do something like:

R> wt %*% ifelse(wt, x, 0)
     [,1]
[1,]    3

Andy 

 
> Alberto Monteiro
> 
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