Number of unique firms/ industries

[Helen Chang]

Hi I have a panel data. Gvkey is an identifier for firms and Fyear is an identifier for year. Sic is used to identify industry.

How can I get the number of unique firms or the number of unique industries in my sample?

Thank you in advance for your help!

[Carlo Lazzaro]

Helen:
you may want to try something along the following lines:

. use "https://www.stata-press.com/data/r16/nlswork.dta"
(National Longitudinal Survey.  Young Women 14-26 years of age in 1968)

. egen counter=tag(idcode)

. count if counter==1
  4,711

.

[Nick Cox]

https://www.stata-journal.com/sjpdf....iclenum=dm0042 is a detailed discussion of such matters. Among other things, it discusses a distinct command which must be installed before you can use it.

search distinct, sj

leads to download links, the latest at the time of writing being


SJ-15-3 dm0042_2 . . . . . . . . . . . . . . . . Software update for distinct
(help distinct if installed) . . . . . . N. J. Cox and G. M. Longton
Q3/15 SJ 15(3):899
improved table format and display of large numbers of
observations

Here is distinct in action:

. webuse grunfeld, clear

. distinct company year

--------------------------------
         |     total   distinct
---------+----------------------
 company |       200         10
    year |       200         20
--------------------------------

. distinct

--------------------------------
         |     total   distinct
---------+----------------------
 company |       200         10
    year |       200         20
  invest |       200        195
  mvalue |       200        198
  kstock |       200        199
    time |       200         20
--------------------------------

[Helen Chang]

Thank you!! It works perfectly!