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


From   Martin Weiss <martin.weiss@uni-tuebingen.de>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: is this a missing value issue? (-if- command used)
Date   Mon, 21 Jul 2008 15:26:37 +0200

The -if- loop watches out for the first value of `var'. If that is below 0.1, it drops the value. As you say, most of the zts contain a missing as their first value which counts as infinitely large in Stata. So when Stata evaluates the if condition, it does not drop, and this behaviour is exactly as it should be...
Replacing missings with zeros, the first value of each zt will likely comply with the if statement most of the time, and I am not at all sure whether that is what you want...


Martin


Quoting 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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