st: is this a missing value issue? (-if- command used)

[Andrea Bennett <mac.stata@gmail.com>]

Hi!

I have the following code in my do-file:

qui lookfor zt
qui foreach var of varlist `r(varlist)' {
	if `var'<=.1  {
		drop `var'	
	}
}

All my zt* variables are percentages of missing values of the original  
variables, e.g. zt_age_2000==0.04 means that 0.04 percent of the  
variable age in year 2000 are missing. The way I generated the zt- 
variables, they contain Stata missing values for all years except the  
corresponding year, e.g. in the above case the zt_age_2000 variable  
contains missing values for all years smaller and greater than 2000  
while for the year 2000 it shows the percentage missing.

Now with the above query I want to get rid of zt-variable if their  
missing percentage is below the threshold of 0.1. Strangely, when I  
use the above commands, it does not perform what I want. However, when  
I first recode each zt-variable and set the missing values to zero,  
then the if-query works fine.

So, what am I doing wrong when using the if-command?

Many thanks for your considerations,

Andrea 
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