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Re: st: identifying variables


From   Abhimanyu Arora <abhimanyu.arora1987@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: identifying variables
Date   Mon, 9 Apr 2012 12:12:58 +0200

Thank you for this "squiggly" tidbit, Nick!

On Mon, Apr 9, 2012 at 12:07 PM, Nick Cox <njcoxstata@gmail.com> wrote:
> 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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