On May 12, 2010, at 3:14 PM, Clark Johnston wrote:


Is there a way to create a new matrix from and existing matrix with

A
         [,1]     [,2]
[1,]      1        13
[2.]      2        18
[3,]      3        14
[4,]      4        20

if()

B
      [,1]   [,2]
[1,]   2      18
[2,]   4      20

Try (untested absent reproducible example);

A[A[,2] > 15, ]

This (should) create a logical vector in the first argument to "[" which has the effect of returning the rows for which that vector is TRUE.



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