Hi,

I have a matrix with few hundred by a few hundred and want to extract rows,
e.g. (0,1,0), or (1.3, 2.4, 4). I made an example:

> A = rep(rep(c(0,1),4),2)
> B = rep(rep(c(0,1),each=4),2)
> C = rep(rep(rep(c(0,1),2),each=2),2)
> X = data.frame(A,B,C,rnorm(16))
      A B C
 [1,] 0 0 0  0.72767870
 [2,] 1 0 0 -0.09673298
 [3,] 0 0 1  0.51192790
 [4,] 1 0 1 -1.54350441
 [5,] 0 1 0  0.91775344

In this example, is there a better way of doing 'X[ X$A==1 & X$B == 0 & X$C
==1, 4]' ? I want to find the unique group definition by 'unique' and then
extract rows corresponding each unique vector that is returned by 'unique'
function.

Thanks a lot
Young.

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