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From |
"Martin Weiss" <martin.weiss1@gmx.de> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
st: RE: what does _N mean under by varlist in the -egen- and -gen-? |

Date |
Sat, 8 Aug 2009 14:34:15 +0200 |

<> I can most easily explain (1), (3) and (4), but not (2). In (2), it does indeed seem that the -if- qualifier is evaluated for the overall dataset, and not with respect to the -by- groups. When I change the very last observation in the -input- statement given by gjhxmu, a.k.a. Rose to "0", the -total- statement all of a sudden does produce values instead of missings... ********** 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 0 end bys family: egen x=/* */total(sex) if sex[_N]==0 list, noobs sepby(fam) replace sex=1 in l bys family: egen xx=/* */total(sex) if sex[_N]==0 list, noobs sepby(fam) ********** HTH Martin -----Original Message----- From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of gjhxmu@sina.com 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. * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: what does _N mean under by varlist in the -egen- and -gen-?***From:*gjhxmu@sina.com

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