New on SSC: _gdistinct function to generate a count of distinct values

[Noah Case]

Hi all,

A new egen function is now available on SSC (thanks to Christopher Baum). _gdistinct works with egen to generate a count of the distinct values of a variable list and takes a by option.

Type ssc install _gdistinct to download the package.

Then, you can run commands such as:

bysort varlist1: egen int newvar = distinct(varlist2)

Type help _gdistinct for more information.

After using routines like this several times in my work, I figured that this might be useful to others.

[Nick Cox]

Thanks for this contribution! It's a good name.


Compare also this function, which is part of egenmore on SSC. It does date from the time before a by prefix become standard, but the option gives the same functionality.

. ssc type _gnvals.ado
*! 1.0.1 NJC 20 November 2000
*! 1.0.0 NJC 20 July 2000
program define _gnvals
        version 6
        gettoken type 0 : 0
        gettoken g 0 : 0
        gettoken eqs 0 : 0

        syntax varlist [if] [in] [, by(varlist) MISSing]
        tempvar touse
        quietly {
                mark `touse' `if' `in'
                if "`missing'" == "" {
                        markout `touse' `varlist', strok
                }
                sort `touse' `by' `varlist'
                by `touse' `by' `varlist': gen `type' `g' = _n == 1 if `touse'
                by `touse' `by' : replace `g' = sum(`g') if `touse'
                by `touse' `by' : replace `g' = `g'[_N] if `touse'
                
        }
end

In https://www.stata-journal.com/articl...article=dm0042 we showed that a combination of egen, tag() and egen, total() would get you there, thus combining official functions and not obliging any installation.

Other way round, a distinctgen command was part of a later update to that sequence.

SJ-23-4 dm0042_5  . . . . . . . . . . . . . . . . Software update for distinct
        (help distinct, distinctgen if installed)  N. J. Cox and G. M. Longton
        Q4/23   SJ 23(4):1096
        comments out (and thus removes) a call to clear Mata at the
        close of work, which was frustrating some other projects
        also using Mata

SJ-23-2 dm0042_4  . . . . . . . . . . . . . . . . Software update for distinct
        (help distinct, distinctgen if installed)  N. J. Cox and G. M. Longton
        Q2/23   SJ 23(2):595--596
        most important change is addition of distinctgen command