Re: st: generate variable equal to first non-zero value in row

[Nick Cox <njcoxstata@gmail.com>]

(Revised version, thanks to comments by Eric Booth)

Nick
njcoxstata@gmail.com

How would you do it by hand? You would look at each variable from left
to right until you find the first non-zero. So, Stata can be
instructed to do that too.

This code assumes no missings in -out*-. If missings are present, add
an extra condition -!missing(out`j')-.

gen first_nz = .
gen where_first_nz = .

qui forval j = 1/5 {
        replace first_nz = out`j' if out`j' & first_nz == .
        replace where_first_nz = `j' if out`j'  & where_first_nz == .
}

Note here that

 if `outj'

is short-hand for

if `outj' != 0

and we also need conditions such as

first_nz == .

If all values are zero, both variable remain set to missing.
>
> For a fairly detailed review of such questions, see
>
> SJ-9-1  pr0046  . . . . . . . . . . . . . . . . . . .  Speaking Stata: Rowwise
>         (help rowsort, rowranks if installed) . . . . . . . . . . .  N. J. Cox
>         Q1/09   SJ 9(1):137--157
>         shows how to exploit functions, egen functions, and Mata
>         for working rowwise; rowsort and rowranks are introduced
>
> which is accessible at http://www.stata-journal.com/sjpdf.html?articlenum=pr0046
> Nick
> njcoxstata@gmail.com
>
>
> On 21 August 2013 16:25, D-Ta <altruist81@gmx.de> wrote:
>> Dear Statausers,
>>
>> I have a dataset with the variables id and and out1-out5 where the "out"
>> variables represent sequential outcomes. I would like to generate a variable
>> (in the example below named first_nonzero) which indicates the first outcome
>> in the sequence row that is non zero. If there are all zeros throughout,
>> that indicator variable should be set/remain missing.
>>
>> The following table illustrateswhat I am trying to do. How do I generate the
>> first_nonzero variable? (I was trying to work with the -egenmore- commands,
>> but couldnt figure out).
>>
>> id      out1    out2    out3    out4    out5    first_nonzero
>> 1       0       0       0       2       2       2
>> 2       0       2       2       0       0       2
>> 3       0       0       0       0       0                             .
>> 4       4       4       4       0       0       4
>> 5       3       0       2       2       2       3
>> 6       0       4       4       4       0       4
>>
>>
>> Many thanks,
>> Darjusch
>> *
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