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RE: st: Creating id number by subgroup


From   "Nick Cox" <[email protected]>
To   <[email protected]>
Subject   RE: st: Creating id number by subgroup
Date   Tue, 6 Jan 2009 19:41:18 -0000

Another solution in the same spirit: 

sort id , stable 
by id : gen var1 = sum(title != title[_n-1]) 

Every time that -title- changes, the identifier is incremented by 1. 

This works for the first observation in each panel too, as title[1]
differs from title[0] which is taken to be missing. 

For much more detail on this approach, see 

SJ-7-2  dm0029  . . . . . . . . . . . . . . Speaking Stata: Identifying
spells
        . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N.
J. Cox
        Q2/07   SJ 7(2):249--265                                 (no
commands)
        shows how to handle spells with complete control over
        spell specification

Nick 
[email protected] 

Maarten L. Buis

bys id title : gen byte notfirst = !(_n==1)
bys notfirst id (title): gen tid = _n if notfirst == 0
bys id title (notfirst): gen id2 = sum(tid)
*-------------------- end example ----------------------
(For more on how to use examples I sent to the Statalist, see
http://home.fsw.vu.nl/m.buis/stata/exampleFAQ.html )

Mike Kim

> I would like to create 'var1' in the following table based on id and
> title.

<snip>

> id  title  var1  var2
> 1    A      1    1
> 1    A      1    2
> 1    B      2    1
> 1    B      2    2
> 1    B      2    3
> 2    C      1    1
> 2    C      1    2
> 2    C      1    3
> 2    D      2    1
> 2    D      2    2
> 3    E      1    1

*----------------- begin example -------------
drop _all

input id  str1 title  var1  var2
1    A      1    1
1    A      1    2
1    B      2    1
1    B      2    2
1    B      2    3
2    C      1    1
2    C      1    2
2    C      1    3
2    D      2    1
2    D      2    2
3    E      1    1
end

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