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Re: st: Use extended functions outside of macro assignment?


From   Nick Cox <njcoxstata@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Use extended functions outside of macro assignment?
Date   Wed, 7 Sep 2011 07:06:33 +0100

The logic of -list- with -if- is like any other command. Consider

list if 2 == 2

2 == 2 is (vacuously) true when considered for observation 1, for
observation 2, and so on, so every variable and every observation will
be -list-ed. The same will be true of your syntax. If your condition
is true, i.e. there is a match, then everything will be listed.

What I think you want is a two-step operation to Stata. First, you
produce a varlist, then you supply that varlist to some command. In
official Stata, check out -ds- and in user-written Stata check out
-findname-. -search findame- in an up-to-date Stata will find an
article and an update in the Stata Journal; use the update to get the
software and read the article!

Nick

On Tue, Sep 6, 2011 at 9:06 PM, James Sams <sams.james@gmail.com> wrote:
> I keep running into situations where I would like to use an extended function
> as a part of a function call, e.g. in a conditional statement. I thought I had
> seen syntax to do this before, but I cannot find this now.
>
> For example, let's say I wanted to operate on a set of observations dependent
> upon some characteristic of a value label, say that the value label matches
> some regular expression. How can I do this? I specifically cannot pull the value
> label into a string variable with decode due to the size of the dataset:
>
> Something like this:
> list if regexm("`: label (varname)'", "my_regex")
>
> or say I want to operate on a set of ids I have stored in a local macro "ids":
>
> list if `: list posof id in ids'
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