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Re: st: identifying variables


From   Nick Cox <njcoxstata@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: identifying variables
Date   Mon, 9 Apr 2012 11:07:54 +0100

You can do it this way

foreach v of var * {
         capture if strpos(`v'[1], "real") {
                         local vars `vars' `v'
         }
}

The { } are best called braces or curly brackets. Parentheses are
strictly (). See e.g.

http://www.catb.org/jargon/html/A/ASCII.html

for a useful glossary. (The entire site is superb.)

Nick

On Mon, Apr 9, 2012 at 10:56 AM, Abhimanyu Arora
<abhimanyu.arora1987@gmail.com> wrote:
> Very useful to know, Nick. Just to confirm, in general stata goes
> further into the command only if the _if_ condition returns 1. There
> is no need for parenthesis or a separate line for -local-. Thanks for
> this detail.
> Cheers
> Abhimanyu
>
>
> On Mon, Apr 9, 2012 at 11:33 AM, Nick Cox <njcoxstata@gmail.com> wrote:
>> Note also that a solution from first principles is also possible:
>>
>> foreach v of var * {
>>        capture if strpos(`v'[1], "real") local vars `vars' `v'
>> }
>>
>> di "`vars'"
>>
>> You need the -capture- unless all the variables are string.
>>
>> Nick
>>
>> On Mon, Apr 9, 2012 at 8:57 AM, Nick Cox <njcoxstata@gmail.com> wrote:
>>> You have provided yet another example of a problem in which -strpos()-
>>> offers a simple alternative to -regexm()-.
>>>
>>> That aside, your syntax is looking for the string "real" in the
>>> _variable names_ themselves, for which
>>>
>>> . findname *real*
>>>
>>> would be a more obvious syntax, and indeed -describe *real*- would
>>> work fine. Stata has a similar distinction in all string and regular
>>> expression functions between looking in a string variable strvar and
>>> looking in a variable name "varname".
>>>
>>> . l in 1
>>>
>>>     +-------------------------------------------+
>>>     |     foo       bar     bazz    y         x |
>>>     |-------------------------------------------|
>>>  1. | reality   surreal   unreal   42   3.14159 |
>>>     +-------------------------------------------+
>>>
>>> . findname in 1, all(strpos(@, "real"))
>>> foo   bar   bazz
>>>
>>> . findname in 1, all(regexm(@, "[real]"))
>>> foo   bar   bazz
>>>
>>> . findname in 1, all(regexm(@, "real"))
>>> foo   bar   bazz
>>>
>>> @ is the default generic varname. -placeholder()- lets you specify an
>>> alternative. You only need to specify "@" for searching the variable
>>> names, but as above there are easier ways to do that.
>>>
>>> Nick
>>>
>>> On Mon, Apr 9, 2012 at 3:50 AM, Abhimanyu Arora
>>> <abhimanyu.arora1987@gmail.com> wrote:
>>>
>>>> I need to identify the variables for which the first observation
>>>> contains the string "real".
>>>> I used Nick Cox's -findname- from the SSC (updated 27 February 2012)
>>>> in the following command.
>>>>
>>>> findname var1-var56 in 1,all(regexm("@","real+")) loc (varnames)
>>>>
>>>> But since -return list- comes up empty, something is amiss, perhaps in
>>>> the use of the regular expression. May I also request some clarity in
>>>> understanding of the role played by a "placeholder" in -findname-? As
>>>> I see it, a generally character designated as a "placeholder" is
>>>> supposed to take on supplied values—string or numerals. Or in other
>>>> words, how would stata read the "@" in the above command?
>>>>
>>
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