st: RE: Mata equivalent for R's which() or matlabs find() functions?

[Nick Cox <n.j.cox@durham.ac.uk>]

I think the test is whether what is needed can be written if there is no obvious candidate. Perhaps there is; but here is a sketch:

real colfind(transmorphic matrix M, transmorphic colvector v) { 

real j 
rowvector indices
indices = J(1,0,.) 

for(j = 1; j <= cols(M); j++) { 
	if (M[,j] == v) indices = indices , j 
}

return(indices) 

}

: y = J(4,2,(1..4))

: y
       1   2   3   4   5   6   7   8
    +---------------------------------+
  1 |  1   2   3   4   1   2   3   4  |
  2 |  1   2   3   4   1   2   3   4  |
  3 |  1   2   3   4   1   2   3   4  |
  4 |  1   2   3   4   1   2   3   4  |
    +---------------------------------+

: colfind(y, J(4,1,4))
       1   2
    +---------+
  1 |  4   8  |
    +---------+

: text = J(1,4,("foo", "bar"))

: text 
         1     2     3     4     5     6     7     8
    +-------------------------------------------------+
  1 |  foo   bar   foo   bar   foo   bar   foo   bar  |
    +-------------------------------------------------+

: colfind(text, "foo")
       1   2   3   4
    +-----------------+
  1 |  1   3   5   7  |
    +-----------------+

Nick 
n.j.cox@durham.ac.uk 

Sebastian Eppner

I am desperately looking for a Mata function that gives me the column
indices of columns that satisfy certain conditions.

For MATLAB, find() can solve the job. In R, which() does it.

I look for something like this in Mata, but haven't found anything
yet. It seems too basic to not be included...


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