IF EXISTS equivalent when keeping variables

[Daniel Sutcliffe]

Hello,

I have the following loop which reads in multiple files and saves them - I only want to keep certain variables in the files that are read in. All the files will have at least one of the variables listed in the "keep" clause of the code, most will have all three, but some only one, others will have two.

Is there a way to rewrite the code to say, if one or more of the variables listed exist - then keep them? At the moment the code ends in error if one of the variables is not present


foreach x of newlist DEM DEP MH AST COPD CVDPP CAN AF HYP CHD HF STIA RA BP SMOK DPE RTR CHY OSTIA {

use "$path\QOF_`x'.dta", clear
*
keep GPCode Prevalence1920_* PCScore1920_* ExcptRate1920_*

destring _all, ignore(":") replace
save qof_`x'.dta, replace

}

[Carlo Lazzaro]

Daniel:
what about the -no stop- option, -do- file entry, Stata .pdf manual?

[Nick Cox]

Instead of

keep GPCode Prevalence1920_* PCScore1920_* ExcptRate1920_*

do something like this

local varlist 

foreach v in GPCode Prevalence1920_* PCScore1920_* ExcptRate1920_* { 

    capture ds `v'  
    local varlist `varlist' `r(varlist)' 

} 

keep `varlist'

[Archibald Dunlop]

When I need to do this I use the -isvar- package which can accept multiple variables as arguments and return those found in `r(varlist)'.

[Nick Cox]

. ssc desc isvar

--------------------------------------------------------------------------------------------------------
package isvar from http://fmwww.bc.edu/repec/bocode/i
--------------------------------------------------------------------------------------------------------

TITLE
'ISVAR': module to filter names into variable names and others

DESCRIPTION/AUTHOR(S)

isvar takes a list of names that might name variables in your
dataset and filters it into a list of those names that are
indeed variable names and a list of the others.

KW: variable names
KW: data management

Requires: Stata version 8.0

Distribution-Date: 20050921

Author: Nicholas J. Cox, Durham University
Support: email [email protected]


INSTALLATION FILES (type net install isvar)
isvar.ado
isvar.hlp
--------------------------------------------------------------------------------------------------------
(type ssc install isvar to install)