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From |
Matthew White <mwhite@poverty-action.org> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: _N in by-groups |

Date |
Fri, 19 Aug 2011 10:41:44 +0300 |

So if I execute: sysuse auto bys foreign: drop if _n == _N Then two observations are dropped because _N is the number of observations in the by-group. But in this (admittedly silly) example, _N seems to be the number of observations in the data set: program dispby, byable(recall) disp `0' end sysuse auto bys foreign: dispby _N Both times 74 is displayed, instead of 52 in the first by-group and 22 in the second. Thanks, Matt On Fri, Aug 19, 2011 at 10:07 AM, Maarten Buis <maartenlbuis@gmail.com> wrote: > On Fri, Aug 19, 2011 at 2:21 AM, Matthew White wrote: >> If a Stata command has by-groups, it seems like _N is interpreted >> sometimes as the number of observations in the by-group and sometimes >> as the number of observations in the data set. > > If you use the -by :- prefix it is always defined as the number of > observations within each by-group. Stata would be a pretty lousy > program if such a scalar randomly changed meaning... > > If you want the total number of observations than I would just do: > > local Ntot = _N > > or inside a program that previously used -marksample-: > > count if `touse' > local Ntot = r(N) > > later you do > > by <somevar> `touse' : <something using _N and `Ntot'> if `touse' > > Hope this helps, > Maarten > > -------------------------- > Maarten L. Buis > Institut fuer Soziologie > Universitaet Tuebingen > Wilhelmstrasse 36 > 72074 Tuebingen > Germany > > > http://www.maartenbuis.nl > -------------------------- > * > * 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/ > -- Matthew White Evaluation Coordinator Urban Micro-Insurance Project Innovations for Poverty Action +254 (0)701 025 276 mwhite@poverty-action.org * * 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/

**Follow-Ups**:**Re: st: _N in by-groups***From:*Phil Schumm <pschumm@uchicago.edu>

**Re: st: _N in by-groups***From:*Nick Cox <njcoxstata@gmail.com>

**Re: st: _N in by-groups***From:*Maarten Buis <maartenlbuis@gmail.com>

**Re: st: _N in by-groups***From:*Phil Clayton <philclayton@internode.on.net>

**References**:**st: _N in by-groups***From:*Matthew White <mwhite@poverty-action.org>

**Re: st: _N in by-groups***From:*Maarten Buis <maartenlbuis@gmail.com>

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