st: Deleting variables for lack of observations

["Joel Clovis" <joel.clovis@stud.man.ac.uk>]

Dear listers,

I want to delete variables if they do not contain enough observatoins.  I've
tried to make use of Nick Coxs'  npresent & dropmiss (STB-49:dm67 &
STB-60: dm89)  to no avail, some attempts are in the following manner:

foreach var of varlist cba2tfina-region {
            keep `var' if r(npresent)>=30
    }

this brings up invalid syntax, and I'm not sure why and

keep if npresent(lifeinsdensity )<30

results in 0 observations being deleted, even though
npresent(lifeinsdensity ) without keep..returns  lifeinsdensity  10

Can anyone help?  I'm a Stata 7 user

Kind regards

Joel
Joel Clovis
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