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Re: st: nested loops with varying degrees of nesting


From   Nick Cox <njcoxstata@gmail.com>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   Re: st: nested loops with varying degrees of nesting
Date   Tue, 1 Oct 2013 23:19:00 +0100

I would write this in terms of variable loop counts. Assume here that
I, J, K are defined previously.

forval i = 1/`I' {
    forval j = 1/`J' {
         forval k = 1/`K' {

         }
   }
}

If any of the loop counts is 1, there is no great loss. (If absolutely
nothing is done in such a case, condition inside on the loop count
being 2 or more.)

Shorter code and easier to follow.
Nick
njcoxstata@gmail.com


On 1 October 2013 23:04, David Kantor <kantor.d@att.net> wrote:
> Hello all,
> I would like to write a program that involves nested loops, where the degree
> of nesting is flexible.
> Consider the following simplified shell of a program. c1, c2, c3 are options
> that, for each one that is present, an additional a level of looping should
> be invoked.
>
> prog def t1
> syntax , [c1 c2 c3]
>
> if "`c1'" ~= "" {
>         local loop1 "forvalues d1 = 1/4 {"
>         local loop1end "}"
> }
>
> if "`c2'" ~= "" {
>         local loop2 "forvalues d2 = 1/4 {"
>         local loop2end "}"
> }
>
> if "`c3'" ~= "" {
>         local loop3 "forvalues d3 = 1/4 {"
>         local loop3end "}"
> }
>
> `loop1'
> `loop2'
> `loop3'
> disp "`d1' `d2' `d3'"
> `loop3end'
> `loop2end'
> `loop1end'
>
> end
>
> ----
>
> When this runs, with one or more of the c1,c2,c3 options, I get
> unrecognized command:  } invalid command name
> --just the same as when I type
> }
> in the command window.
> Evidently, a macro can stand for a command, but not "}"  -- or "}" is not a
> command..
>
> Does anyone have an Idea of how to accomplish this goal? I do have one idea,
> involving counting the number of loops:
> if num_loops==1 {
>         forvalues d1 = 1/4 {
>         do_stuff
>         }
> }
> else if num_loops==2 {
>         forvalues d1 = 1/4 {
>                 forvalues d2 = 1/4 {
>                 do_stuff
>                 }
>         }
> else if num_loops==3 {
>         forvalues d1 = 1/4 {
>                 forvalues d2 = 1/4 {
>                         forvalues d3 = 1/4 {
>                         do_stuff
>                         }
>                 }
>         }
> }
>
> -- but I'd rather do something more succinct, if possible; my actual program
> may have up to 8 levels of nesting.
> Does anyone have a suggestion?
> (I do have another idea: build the entire nested looping command into one
> macro; I have not tried this yet.)
> I use Stata 10.
> Thanks
> --David
>
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