st: macro loop embedded in macro loop (Jun Xu)

["Arthur Mu" <mystata@hotmail.com>]

All Stata-Users:

I am writing an ado program that one macro loop embedded in another one.  I 
have figured a way around it, but kind of awkward, not sure if there is an 
easy way to do it.

The command will be like:

mycommand var1 var2 var3 var4, model(reg) compare(1 2; 4 2; 3 2)

I just extracted part of the Program that I am having problems with:

*******************************************************
capture program drop mycommand
program define mycommand
	syntax [varlist] ,model(string) compare(string)
	tokenize `compare', parse("  ;  ")
       local i=1

	while "`1'"~=""{
		...Do whatever I want for the macro's in `compare'
               ...
               ...
		tokenize `varlist'
               while "`1'"~=""{

               ...Do whatever I want for the macro's in `varlist'
               }

               tokenize `compare', parse (" ; ")
               local i=`i'+2
		macro shift `i'
          }
end
****************************************************

What I am trying to do with `varlist' within the while loop is to capture 
individual variable information and store it into a matrix.  While the 
`compare' macro list is to run through each pair within "compare (1 2; 4 2; 
3 2)", in which "1 2" encodes two equations by a group variable like female 
vs. male or white vs. black.  The problem here is: first I tokenize compare 
before the first while loop, and within the while loop I have another 
tokenize and the second while loop, which will overwrite the info stored by 
the first tokenize of `compare'.  To restore the order of the tokenized 
`compare', I tokenize compare again and use local i=`i'+2 and macro shift 
`i' to get away with it.  I am not sure if I correctly explained my 
question, which is "is there an easy way around it?  Otherwise if I need to 
have several tokenize and while loop's, then I will have to restore them 
each time as I did?"

Jun Xu
Doctoral Student
Department of Sociology
Indiana University


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