Counting How Many Unique Responses are in a Set of Variables in Stata

[Huda Jabbar]

I have a data set with variables topicname1-topicname10. I would like to create a variable that gives me a count of the number of unique topics each respondent has within those sets of variables without counting missing responses and only counting each topic name once. I want to do this because sometimes topic names repeat, for example topicname1 can be books but then topicname5 can also be books, but in that instance I only want books to be counted once. I have tried multiple ways to do this including turning the wide data set long but no luck, was wondering if anyone knew a good strategy.

[Nick Cox]

It is always a good idea to give a data example.

Section 7 of

SJ-9-1 pr0046 . . . . . . . . . . . . . . . . . . . Speaking Stata: Rowwise
(help rowsort, rowranks if installed) . . . . . . . . . . . N. J. Cox
Q1/09 SJ 9(1):137--157
shows how to exploit functions, egen functions, and Mata
for working rowwise; rowsort and rowranks are introduced

explains the problem and a solution using the egen function rowsvals() in egenmore from SSC.

For why you should say distinct not unique see Section 2 of

SJ-8-4 dm0042 . . . . . . . . . . . . Speaking Stata: Distinct observations
(help distinct if installed) . . . . . . N. J. Cox and G. M. Longton
Q4/08 SJ 8(4):557--568
shows how to answer questions about distinct observations
from first principles; provides a convenience command

* Example generated by -dataex-. For more info, type help dataex
clear
input byte id str5 topic1 str12 topic2 str8 topic3
1 "books" "music"        "football"
2 "books" "books"        "books"   
3 "books" "rock"         "geology" 
4 "Stata" "Stata"        "Stata"   
5 "books" "philanthropy" "Stata"   
end

. egen wanted = rowsvals(topic*)

. l

     +------------------------------------------------+
     | id   topic1         topic2     topic3   wanted |
     |------------------------------------------------|
  1. |  1    books          music   football        3 |
  2. |  2    books          books      books        1 |
  3. |  3    books           rock    geology        3 |
  4. |  4    Stata          Stata      Stata        1 |
  5. |  5    books   philanthropy      Stata        3 |
     +------------------------------------------------+