<>
You can of course form an expression that does yield the correct result:
***
clear
input family sex
1 1
1 1
1 1
2 0
2 1
2 0
2 1
2 0
3 0
3 1
3 0
3 1
3 1
3 1
end
//complex expression fed to -total-
bys family: egen x=/*
*/total(sex*(sex[_N]==0))
//compare with -if- solution
bys family: egen xx=total(sex) /*
*/ if sex[_N]==0
list, noobs sepby(fam)
***
HTH
Martin
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of [email protected]
Sent: Samstag, 8. August 2009 11:40
To: statalist
Subject: st: what does _N mean under by varlist in the -egen- and -gen-?
Dear statalists,
I know that under by varlist: _N is interpreted within each group of
observations, not for the whole dataset.
However, I found the meaning _N in the -egen- is a little different.
Take the following for example,
clear
input family sex
1 1
1 1
1 1
2 0
2 1
2 0
2 1
2 0
3 0
3 1
3 0
3 1
3 1
3 1
end
bys family: g x=sum(sex) if sex[_N]==0
bys family: egen xx=total(sex) if sex[_N]==0
bys family: g xxx=sex[_N]
bys family: egen xxxx=total(sex[_N]==0)
l,sepby(family) noobs
+------------------------------------+
| family sex x xx xxx xxxx |
|------------------------------------|
| 1 1 . . 1 0 |
| 1 1 . . 1 0 |
| 1 1 . . 1 0 |
|------------------------------------|
| 2 0 0 . 0 5 |
| 2 1 1 . 0 5 |
| 2 0 1 . 0 5 |
| 2 1 2 . 0 5 |
| 2 0 2 . 0 5 |
|------------------------------------|
| 3 0 . . 1 0 |
| 3 1 . . 1 0 |
| 3 0 . . 1 0 |
| 3 1 . . 1 0 |
| 3 1 . . 1 0 |
| 3 1 . . 1 0 |
+------------------------------------+
Based on the results, Obviously the meaning of _N in the first two is
different,
while the meaning of _N in the last two is the same.
Could anyone tell me why?
Thank you very much.
Best regards,
Rose.
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