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RE: st: RE: two STATA questions


From   "Ni Frank" <frankflying03@hotmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   RE: st: RE: two STATA questions
Date   Wed, 28 Feb 2007 02:15:56 -0500

Got it. You are right. I was thinking about the second quetion which keeps those observations at least one of variables is zero.

Thanks again!

Frank


From: "Nick Cox" <n.j.cox@durham.ac.uk>
Reply-To: statalist@hsphsun2.harvard.edu
To: <statalist@hsphsun2.harvard.edu>
Subject: RE: st: RE: two STATA questions
Date: Tue, 27 Feb 2007 09:49:33 -0000

Wrong. -drop if count- is equivalent to -drop if count != 0- which in this
case would only arise -if count > 0-.

Besides, you asked for -drop-ping or -keep-ing if and only if at least
one variable were zero. The variable -count- is a count of the number
of variables in which values are zero in each observation. So,

drop if count == 0

would -drop- only those observations in which no values were zero.

There is more on constructs like -if count- in

FAQ . . . . . . . . . . . . . . . . . . . . . . . True and false in
Stata
        2/03    What is true and false in Stata?
        http://www.stata.com/support/faqs/data/trueorfalse.html

Nick
n.j.cox@durham.ac.uk

Ni Frank

>    Oh,I see. By the way, the "drop if count" should be "drop
> if count==0",
> right? I have tried your method. It works. Thanks very much!

Nick Cox

> > > 1) There are 50 varialbes, w05100, w05200,....,w10000. We
> > > want to DROP
> > > those obversations for which at least one of the above
> > > variables takes
> > > value of 0.  When I use "drop if w*==0, it said "W* invalid name".
> > > Does anybody know what's wrong?
> >
> >That's illegal. You can't put a wildcard there after -if-.
> An expression
> >can go there, but a wildcard doesn't qualify as an expression.
> >
> >Here is one way to do it.
> >
> >gen byte count = 0
> >
> >qui forval i = 5100(100)10000 {
> >	replace count = count + (w0`v' == 0)
> >}
> >
> >drop if count
> >
> > > 2)  Now, if we want to KEEP those obersvations for which
> at least one
> > > of the variables w05100, w05200, ....,w09900 takes value
> of 0. How to
> > > do that?
> >
> >It's the same story, except for -keep- instead of -drop-.

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