How to make a macro to loop through two non consecutive months?

[Shradha1]

I am doing an analysis on data for 3 specific months: 202006, 202007, 202008.

And for each of these 3 months, I want a macro loop, which will run only for M-1 and M+6 month where M takes the above three months as values. The starting part of my macro is this:

%LET Mon_ST = 202006;			
%LET Mon_EN = 202008;			
Option obs = Max;			
			
%macro copy_data();			
			
%DO Mnth = &Mon_ST. %TO &Mon_EN. ;			
%IF %SUBSTR(&Mnth.,5,2) = 13 %THEN %LET Mnth =	%EVAL(%SUBSTR(&Mnth.,1,4)+1)01;	
%Put Mnth = &Mnth.;	

Now, I want to create another loop within this macro which will run for only two specific time periods for each of these months. For eaxample, when Mnth =202006, the loop will create another macro variable, say MON, which will first take value 202005 (Mnth-1) and on the next iteration will take value 202012 (Mnth+6). Similary, when Mnth =202007, MON will first be equal to 202006, and then 202101.

How do I create this sub loop? Any help will be much appreciated. Thanks!

[ChrisNZ · Accepted solution]

One way:

%let mon_st = 202006;			
%let mon_en = 202008;			
option obs = max;			
			
%macro copy_data();			
  %local mnth from to by m;
  %do mnth = &mon_st. %to &mon_en. ;			
    %if %substr(&mnth.,5,2) = 13 %then %let mnth = %eval(&mnth+100-12);	
    %put &=mnth;
    %let from= %sysfunc(intnx(month,%sysfunc(inputn(&mnth,yymmn6.)),-1),yymmn6.); 	
    %let to  = %sysfunc(intnx(month,%sysfunc(inputn(&mnth,yymmn6.)),+6),yymmn6.);
    %let by  = %eval(&to - &from);
    %do m=&from %to &to %by &by;
      %put &=m;
    %end;
  %end;
%mend;
%copy_data;

MNTH=202006
M=202005
M=202012
MNTH=202007
M=202006
M=202101
MNTH=202008
M=202007
M=202102