Re: st: Create the count of occurances in a panel

[Matt Dobra <mattdobra@gmail.com>]

If the variable name for your ids is "id", and assuming your variable 
for years is named "year", you could do:

collapse (count) year, by(id)

Which would turn (making up numbers for years here), for example:

id    year
4001    1990
4001    1991
4001    1992
4002    1990
4002    1991
4003    1992
4003    1993
4003    1994
4003    1995
4004    1992
4004    1993
4004    1994
4008    1998
4172    1995
4172    1996

into

id    year
4001    3
4002    2
4003    4
4004    3
4008    1
4172    2

Matt

wying1@umbc.edu wrote:


> Dear users,
>
> I have a list of person ids as follows.
>
>   1.         4001
>   2.         4001
>   3.         4001
>   4.         4002
>   5.         4002
>   6.         4003
>   7.         4003
>   8.         4003
>   9.         4003
>  10.         4004
>  11.         4004
>  12.         4004
>  13.         4008
>  14.         4172
>  15.         4172
>
>  The number of occurances represents the years they are in a panel
> dataset.  For example, person 4001 have appeared three years in the
> panel, and person 4003 has occured four years in the panel.
>
> I am trying to create a count of years those individuals occur in the
> panel, i.e., 3 for person 4001, 4 for person 4003, 3 for person 4004, 1
> for person 4008, etc.  I have some thoughts to do this by reshaping the
> data, but doubt that is the most efficient way to do. Is there any fast
> way to do it in STATA?
>
>
> Thanks,
> Ying
>
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