[R] mask a matrix

[Liaw, Andy]

If you just multiply the two together, you get 0 in the right positions.  If
you want those to be NAs, just do:

result <- ifelse(A, B, NA)

Andy

> From: Lei Jiang
> 
> Hi, there.
> 
> I have two matrix with identical dimentions. matrix A contains 
> information of 0 and 1, and matrix B contains data. I only 
> want the data 
> in matrix B where matrix A has 1's. the places where matrix A 
> has 0's, I 
> want NA's in matrix B.
> 
> How do I do that??
> 
> Thank you very much.
> 
> Lei Jiang
> 
> Department of Chemsitry
> University of Washington
> Box 351700
> Seattle, WA 98195
> Phone: 206-616-6882
> Fax: 206-685-8665
> 
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