On 20/01/2009, at 9:48 AM, Andrej Kastrin wrote:
Dear all,
Suppose that I have a matrix A
A <- matrix(c(3,3,3,3,3,3,3,3,3),3,3)
and a logical matrix B
B <- matrix(c(T,T,T,F,T,T,F,T,F),3,3)
The result matrix should be
C <- matrix(c(3,3,3,NA,3,3,NA,3,NA),3,3)
Is there any simple tip or trick to perform this without looping?
(a) It is helpful to state a clear question rather than expecting the
reader to infer from an example just what your question is.
(b) It is advisable to use TRUE and FALSE as the values of a logical
variate, rather than T and F. The former are reserved words, the latter
are not, which can cause all hell to break loose.
(c) You are wasting a good many key strokes. You could simply say
A <- matrix(3,3,3)
(d) I infer that what you want is for C to equal A where B is TRUE
and NA otherwise. One way to accomplish this is:
C <- matrix(,3,3)
C[B] <- A[B]
cheers,
Rolf Turner
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