Re: st: loop thru unique values of a variable

[Roger Newson <roger.newson@kcl.ac.uk>]

At 17:32 06/09/02 -0700, Matt Schonlau wrote:
> Hi all !
>
> I am trying to loop through all unique values of a variable.
>
> For example if the data set contains 9 observations and the variable of 
> interest is D which takes the values 0 0 0 2 2 2 4 4 4
> I would like to loop through the unique values 0 2 4  .
>
> Below is a terrible "fix" which makes the additional assumption that the 
> unique values are evenly spaced. ( I prefer not to make that assumption). 
> It basically extracts the number of unique values from *inspect*, finds 
> the minimum value through *summarize* and then constructs the loop from 
> scratch .
>
> quietly inspect D
> local nu=r(N_unique)
> quietly sum D
> local dmin = r(min)
> local last = `nu' * `dmin'
>
> forvalues d= `dmin'(`dmin') `last' {
> ...
> }
>
> Is there a better way to do that in stata or is that just not what stata 
> was built for ?
I would use Nick Cox's -vallist- package, downloadable from SSC. In 
Web-aware Stata, type -findit vallist- or -ssc describe vallist- to find 
out more.

For instance, Matt might type

vallist D
local values "r(list)"
foreach d of numlist `values' {
...
}

where ... again stands for whatever Matt wanted to do for each value.

I hope this helps.

Roger


--
Roger Newson
Lecturer in Medical Statistics
Department of Public Health Sciences
King's College London
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Email: roger.newson@kcl.ac.uk

Opinions expressed are those of the author, not the institution.

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