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RE: st: dropping variables


From   "Nick Cox" <[email protected]>
To   <[email protected]>
Subject   RE: st: dropping variables
Date   Thu, 18 Mar 2004 11:58:12 -0000

is to -drop- all string variables, 
as r(N) is returned as 0. 

Nick 
[email protected] 

> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of Nick Cox
> Sent: 18 March 2004 11:50
> To: [email protected]
> Subject: RE: st: dropping variables
> 
> 
> A problem with Dimitry's loop is that it will crash 
> the first time it hits a string variable. I would 
> tune it to 
> 
> foreach v of var * { 
> 	qui count if !missing(`v') 
> 	if r(N) < 100 drop `v' 
> } 
> 
> where 100 is of course a place-holder for your own 
> desired constant. 
> 
> -count- remains an under-appreciated command. 
> 
> Nick 
> [email protected] 
> 
> Dimitriy V. Masterov
>  
> > There might be a more clever way of doing this, but here's my 
> > solution:
> > 
> > /* This defines a local named variables that contains a list 
> > with all variables */
> > unab variables:  _all
> > 
> > /* This loop drops all variables that have fewer than 100 obs. */
> > foreach var in `variables' {
> > qui sum `var'
> > 	if r(N)<100 {
> > 		drop `var'
> > 	}
> > }
> 
> Eric Uslaner
> 
> > > I know of Nick Cox's great dropmiss program.  I want to 
> do something
> > > akin to it (without having to drop each variable 
> individually).  Say
> > > that a data set has N cases and I want to drop variables 
> > that have fewer
> > > than n nonmissing cases.  Theoretically I could generate 
> > new variables
> > > through count, but my data set is already close to the 
> > maximum allowed
> > > without upgrading to SE (which is why I want to drop some 
> > variables).
> > > Is there a way to do this:
> > >
> > > drop if _N < n
> > >
> > > or something similar?
> 
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