Count unique numbers of a varlist

[Cong Gu]

Dear statalists,

I have following dataset and would like to count the unique number (remove duplicates) of analyst (according to the analyst code) with respect to the firm for each year.

firm id	analyst code	year
00130H10	9494	1996
00130H10	7422	1996
00130H10	1.80E+04	1996
00130H10	9946	1996
00130H10	3.20E+04	1996
00130H10	9946	1996
00130H10	3.20E+04	1996
00130H10	3.10E+04	1996
00130H10	9932	1996
00130H10	7422	1996
00130H10	3.20E+04	1996
00130H10	9932	1996
00130H10	3.10E+04	1996
00130H10	7422	1996
00130H10	0	1997
00130H10	1.80E+04	1997
00130H10	9946	1997
00130H10	9946	1997
00130H10	1646	1997
00130H10	556	1997
00130H10	3.10E+04	1997
00130H10	9494	1997
00130H10	3.20E+04	1997
00130H10	3.10E+04	1997
00130H10	1112	1997
00130H10	9494	1997
00130H10	9946	1997
00130H10	3.20E+04	1997
00130H10	1112	1997

Many thanks in advance.

Best!!

[Charlie Joyez]

There is plenty of ways to do this, and it all depends on what you want.
If you just want the number to be displayed, just use the user written -distinct- command, available on SSC.

If you want this number to be saved in a variable, use the egen, nvals() command.

Anyway, you everything you need is written here :
http://www.stata.com/support/faqs/da...-observations/

Charlie

[Carlo Lazzaro]

Cong:
what follows can do the trick:

bysort analystcode: keep if [_n]==1

[Nick Cox]

Cong: You got good advice, except that your data appear messed up and it is probably unwise to do anything until that is reversed.

Your analyst code variable looks like a string variable and has values like "1.80E+04". Here E indicates 10, so 1.80E+04 could be any integer from 17500 to 18499, or so I guess, so distinct codes may well have got mushed together.

On the program distinct, the Stata Journal references given below are clickable if you repeat the command in Stata:

.        search distinct, sj

Search of official help files, FAQs, Examples, SJs, and STBs

SJ-12-2 dm0042_1  . . . . . . . . . . . . . . . . Software update for distinct
        (help distinct if installed)  . . . . . .  N. J. Cox and G. M. Longton
        Q2/12   SJ 12(2):352
        options added to restrict output to variables with a minimum
        or maximum of distinct values

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

[Cong Gu]

Dear Charlie, Carlo and Nick, many thanks for your kind help.