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# st: bys and [_N] within replace

 From To Subject st: bys and [_N] within replace Date Wed, 18 Mar 2009 11:05:24 +0100

I have the following panel.

Id	Commdate	Result2
400	05may2008	TM FAILURE
400	29may2008	DM FAILURE
400	05oct2008	TM Ei-svar
400	27oct2008	TM Ei-svar
400	30nov2008	TM Ei-svar
400	04jan2009	TM Ei-svar

I would like to generate a binary variable that equals 1 if a category "TM Ei-svar" within result2 occurs. But I only want this to happen if no other category in Result2 is present within Id, either onwards are backwards in time (Commdate). Nick Cox and Martin Weiss gave excellent advice on an earlier related problem pointing me to 'bys' and using [_N] within replace statements. Nick also refered me to further free 'by' tricks at

http://www.stata-journal.com/sjpdf.html?articlenum=pr0004

However, I am still unable to solve the above problem. I tried

gen kun_eisvar=0
bys Id (Commdate):replace kun_eisvar=1 if ///
(result2=="TM Ei-svar"& ///
result2[_N]!="TM FAILURE"&result2[_N-1]!="TM FAILURE"& ///
result2[_N]!="TM SUCCESS"&result2[_N-1]!="TM SUCCESS"& ///
result2[_N]!="SUCCESS DM SMS 1999"&result2[_N-1]!="SUCCESS DM SMS 1999"& ///
result2[_N]!="DM SUCCESS NY BIND"&result2[_N-1]!="DM SUCCESS NY BIND"& ///
result2[_N]!="DM SUCCESS"&result2[_N-1]!="DM SUCCESS"& ///
result2[_N]!="DM FAILURE"&result2[_N-1]!="DM FAILURE")

though, this does not work. See an example below.

Id	Commdate	Result2	kun_eisvar
400	05may2008	TM FAILURE	0
400	29may2008	DM FAILURE	0
400	05oct2008	TM Ei-svar	1
400	27oct2008	TM Ei-svar	1
400	30nov2008	TM Ei-svar	1
400	04jan2009	TM Ei-svar	1

Because Result2 has other categories than 'TM Ei-svar' for Id=400 this observation should not equal 1.

Any advice on where I went wrong is appreciated.

Best wishes,
Alexander

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