Jiang,
This example could help:
 
A <- matrix(rbinom(20,1,.8),ncol=2)
B <- cbind(rnorm(20,-1,0),rnorm(20,1,0))
B <- ifelse(A==0,NA,B)
B
A
 
 
S M Mwalili.

Lei Jiang <lj22@u.washington.edu> wrote:
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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