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RE: st: keeping dates which are n periods apart


From   "Rajesh Tharyan" <R.Tharyan@exeter.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: keeping dates which are n periods apart
Date   Mon, 19 May 2008 09:51:07 +0100

clear
input id year

        4   1987
	  4   1993
        4   1994
        9   1986
        9   1987
        9   1988
        9   1989
        9   1990
        9   1992
        9   1993
        9   1994
        9   1995
        9   1996
        9   1997
end

bysort id (year): gen tag = 1 if _n ==1
bysort id (year): replace tag = 1 if  mod(year, 3) ==1 & tag == . &
tag[_n-1] != 1
keep if tag ==1
drop tag
l, sepby(id)

gives me

    id   year  
     4   1987  
     9   1986  
     9   1990  
     9   1993  
     9   1996  

It dosent keep the year 1993 for id  4

Thanks
rajesh


-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Scott Merryman
Sent: 19 May 2008 02:50
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: keeping dates which are n periods apart

Does this work?

clear
input id year

        4   1987
        4   1988
        4   1989
        4   1990
        4   1992
        4   1993
        4   1994
        9   1986
        9   1987
        9   1988
        9   1989
        9   1990
        9   1992
        9   1993
        9   1994
        9   1995
        9   1996
        9   1997
end

bysort id (year): gen tag = 1 if _n ==1
bysort id (year): replace tag = 1 if  mod(year, 3) ==1 & tag == . &
tag[_n-1] != 1
keep if tag ==1
drop tag
l, sepby(id)


Scott




On Sun, May 18, 2008 at 8:02 PM, Rajesh Tharyan <R.Tharyan@exeter.ac.uk>
wrote:
> Hi all,
>
> I have this ( a subset of the original dataset, the original dataset has
> about 6000 ids with an  average of 6 years each)
>
>    id   year
>     4   1987
>     4   1988
>     4   1989
>     4   1990
>     4   1992
>     4   1993
>     4   1994
>     9   1987
>     9   1988
>     9   1989
>     9   1990
>     9   1992
>     9   1993
>     9   1994
>
> I need to keep years if they are more than 2 years apart by company.
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