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From |
Nick Cox <n.j.cox@durham.ac.uk> |

To |
"'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu> |

Subject |
st: RE: MATA function that gives the TRUE indices of a logical object |

Date |
Mon, 7 Feb 2011 16:12:55 +0000 |

I am not aware of anything built-in to Mata [sic; not MATA]. Here is something rough: mata: real matrix which(real matrix x, scalar s) { real scalar i, j real matrix out out = J(0,2,.) for(i = 1; i <= rows(x); i++) { for (j = 1; j <= cols(x); j++) { if (x[i,j] == s) out = out \ (i,j) } } return(out) } end This just does what your example does, modulo some convention about row first or column first. Testing for equality with some non-integer value is a whole heap more problematic. Nick n.j.cox@durham.ac.uk r.a.nobel@umail.leidenuniv.nl I have the following question on a function which a want to use in MATA. I think it's best illustrated with an example. In the R-language you have the which() function, which works as follows. Suppose you have a matrix Z: 0 0 0 1 0 0 0 1 0 9 9 1 9 9 9 9 9 9 then using which(Z==9, arr.ind = T) finds entries with Z=9 and returns an array with coordinates as follows: row col 4 1 5 1 6 1 4 2 5 2 6 2 5 3 6 3 Does a similar function exist in MATA? * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: MATA function that gives the TRUE indices of a logical object***From:*r.a.nobel@umail.leidenuniv.nl

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