Re: st: doubt on Mata using multiple loops

["Joseph Coveney" <jcoveney@bigplanet.com>]

A matrix of (mutual) connections ought to be symmetric.  That and a couple of
other things that dawned on me are cleaned up below.  If your firm information
is strings (firm names) instead of numbers, then you could either -encode- or
substitute _st_sdata() and st_sdata() in the inner loop.

Joseph Coveney

version 11.0

clear *
set more off
input byte firm_nr byte connection1 byte connection2
1 5 3
2 0 0
3 1 0
4 2 0
5 1 0
end

list , noobs abbreviate(15) separator(0)

mata
mata set matastrict on

real matrix function getConnectedFirms(| real scalar show_duplicates) {

    show_duplicates = (args() == 0) ? 1 : show_duplicates  // Opt-out

    real scalar observation_tally
    observation_tally = st_nobs()

    real matrix Results
    Results = J(observation_tally, observation_tally, 0)

    real scalar connection_nr, firm_nr // Indexes

    for (connection_nr=2; connection_nr<=st_nvar(); connection_nr++) {

        for (firm_nr=1; firm_nr<=observation_tally; firm_nr++) {
            Results[firm_nr, .] = Results[firm_nr, .] +
              (_st_data(firm_nr, 1) :== st_data(., connection_nr)')
        }
    }
    Results = Results + Results'

    if (show_duplicates) {
        return(Results)
    }
    else {
        return(Results :> 0)
    }
}

getConnectedFirms()
getConnectedFirms(0)
getConnectedFirms(1)

end

exit


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