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Re: using -cond- to create a indicator [was: Re: st: intcens: how to estimate mean and variance after intcens]


From   Nick Cox <njcoxstata@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: using -cond- to create a indicator [was: Re: st: intcens: how to estimate mean and variance after intcens]
Date   Fri, 26 Oct 2012 08:59:22 +0100

Although I am fond of -cond()- I would usually write here

generate wcgrp =  wc>90&sex==1 | wc>80&sex==2   if  wc < .

Nick

On Fri, Oct 26, 2012 at 8:37 AM, Maarten Buis <maartenlbuis@gmail.com> wrote:
> On Fri, Oct 26, 2012 at 6:22 AM, PHAM Ngoc Minh wrote:
>> I wish to create dummy variables containing missing (.), and thus used
>> formula COND(IF, THEN, ELSE) but missing (.) no longer existed. An example
>> as follows:
>>
>> I need to generate (wcgrp) from waist circumference (wc) as 1, 0 or missing
>> (.), then typed:
>>
>> generate wcgrp = cond(wc>90&wc!=.&sex==1|wc>80&wc!=.&sex==2, 1, 0)
>>
>> but (wcgrp) had only 1 and 0, and missing was regarded as 0.
>
> What you want is a new variable that contains three possible values
> (0, 1, .) but you give it values using a function that can only output
> 2 values (one for when the expression is true and one for when the
> expression is false), so that cannot work. Notice however that
> -cond()- is working correctly in the sense that it did exactly what
> you told it to do: it gives a 0 when the expression is false and the
> expression is false when either the waist circumference is smaller
> than some sex specific threshold or when wc is missing.
>
> Below are two possible solutions:
>
> generate wcgrp = cond(wc>90&sex==1|wc>80&sex==2, 1, 0) if !missing(wc)
>
> generate wcgrp = cond(wc>90&sex==1|wc>80&sex==2, cond(missing(wc), ., 1), 0)
>
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