Re: st: conditional "keep" statement

[David Kantor <kantor.d@att.net>]

At 09:54 AM 4/12/2010, David Souther wrote:
> I'm combining (append & merge) hundreds of files which contain
> hundreds or thousands of variables each, and at each stage of the
> merge/append, I'd like to variables only if they are in a list that I
> specify.
> The issue is that not all of these datasets contain all the variables
> in this list.  So, if I create a macro of my list,
>
> local myvars  a1 a2 a3 d1 d2 d3
>
> and then specify,
>
> keep `myvars'
>
> in the loop for each combination of data, I get the error that some
> variable doesn't exist when it's not in the dataset.  I tried getting
> around this with the -capture- command,
>
> cap keep `myvars'
>
> and using -ds-
>
> ds `myvars'
> keep `r(varlist)'
>
> or,
>
> ds `myvars', not
> drop `r(varlist)'
>
> and -ds- in combination with -capture- to no avail.   Any other ideas
> (besides specifying the hundreds of variables to keep for each/every
> loop)??
> [...]

Hi.
I'm not sure what to do if you bump into limits of macros, but I 
wonder if you know about macrolists. This may be useful.

local myvars  a1 a2 a3 d1 d2 d3
ds
localdatasetvars "`r(varlist)'"
local commonvars : list myvars & localdatasetvars

commonvars now contains the variable names common to the dataset and to myvars.

See -help macrolists-.

HTH
--David

*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/