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Re: st: create local with specific value of a variable


From   Pablo Bonilla <pablo.bonilla1234@gmail.com>
To   statalist <statalist@hsphsun2.harvard.edu>
Subject   Re: st: create local with specific value of a variable
Date   Thu, 21 Feb 2013 09:12:05 -0500

Daniel, Jeph and Maarten,

Thank you for your suggestions. All of them very useful.

Best,

On Thu, Feb 21, 2013 at 4:03 AM, Maarten Buis <maartenlbuis@gmail.com> wrote:
> --- On 2/20/2013 10:43 AM, Pablo Bonilla wrote:
>>> Sometimes I need to save in a local a specific value of a variable and
>>> I cannot do it because creating a local does not support “if” neither
>>> “in” conditions. For instances, let’s suppose that I have two
>>> variables: “x” and “y”. Variable “x” goes from 1 to 100 and “y” is a
>>> random vector. Now, how can I save in a local the value of “y” when
>>> “x” is, for example, 50?
>
> --- On Wed, Feb 20, 2013 at 7:09 PM, Jeph Herrin wrote:
>> In a program I would usually do this:
>>
>>  sum y if x==50
>>  local y50 = cond(r(min)==r(max),r(min),.)
>>
>> which also checks that the value is unique.
>
> That is good advise. In a program I would end up adding a bit more
> bells and wistles to it:
>
> You can make this run a bit faster by adding the -meanonly- option to
> -sum-. -novariance- would probably have been a better name for the
> -meanonly- option.
>
> You can store that number with a bit more precision by storing that in
> a scalar. It is almost always a good idea to use  a -tempname- for the
> name of that scalar.
>
> Such a check for equality need to be treated carefully, especially
> when the value is a non-integer, again the problem is precision. I
> also would check if the variable x is not a string variable. For both
> we can use the -`: type <varname>'- extended macro function to extract
> the type of the variable. See -help extended_fcn-.
>
> Taking these points together I would end up with a code like this:
>
> if substr("`: type x'",1,3)!="str" { // check that x is not a string variable
>     if "`: type x'" == "float" { // check if x is stored in float precision
>         sum y if x == float(50), meanonly
>     }
>     else { // x is either an integer or stored in double precision
>         sum y if x == 50, meanonly
>     }
> }
> else {  // x is a string variable
>     sum y if x == "50", meanonly
> }
> tempname y50
> scalar `y50' = cond(r(min)==r(max),r(min),.)
>
> Hope this helps,
> Maarten
>
> ---------------------------------
> Maarten L. Buis
> WZB
> Reichpietschufer 50
> 10785 Berlin
> Germany
>
> http://www.maartenbuis.nl
> ---------------------------------
>
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--
----

Pablo Bonilla

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