ng,
I have a matrix (x) with binary content. Each row of the matrix holds exactly
one 1, and the rest of the row is zeros. The thing is that I need to 'collapse'
the matrix to one column where each row holds the original column index of the
1's (y). Sometimes, the matrix is quite large, so I have a perfomance problem.
x <- matrix(c(1,0,0, 0,0,1, 0,1,0, 0,0,1, 0,1,0, 1,0,0),ncol=3,byrow=T)
x
[,1] [,2] [,3]
[1,] 1 0 0
[2,] 0 0 1
[3,] 0 1 0
[4,] 0 0 1
[5,] 0 1 0
[6,] 1 0 0
In the matrix above, on the first row, the 1 is in column 1, hence '1' on the
first row in the matrix below. On the second row in the matrix above, the 1 is
in column 3, hence the '3' on the second row in the matrix below. And so on...
y
[,1]
[1,] 1
[2,] 3
[3,] 2
[4,] 3
[5,] 2
[6,] 1
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