Teach you write SAS macro: How to split data by every 1000 records?

[Datura]

Question: I have a big data set with 100,000 records, I want to break it into 100 datasets by every 1000 records. How to do it?

Step 1: Fulfill the task with standard code

 Data Z1  Z2  Z3.... Z100;
 Set AAA;
 If _N_=1-1000 then output Z1;  --- I=1
 If _N_=1001-2000 then output Z2; --- I=2
 If _N_=2001-3000 then output Z3; --- I=3
 ..........
 If _N_=99001-100000 then output Z100 --- I=100
 Run;

Step 2: Convert Macro Codes

%macro cover();
 %local I;
 data
 %do I=1 %to 100;
 BBB&I 
 %end;
 ;
 set AAA;

 %do I=1 %to 100;
 if _n_/1000<=&I and _n_/1000>&I-1 then output BBB&I;
 %end;
 run;
%mend;
%cover;

Improved Method I:

 %macro subgroup;
 %local I;
 %do I=1 %to 100;
 data Z&I;
 set AAA;
 if _N_ LE &I*1000 and _N_ GT (&I-1)*1000 then output;
 else delete;
 run;
 %end;
 %mend;
 %subgroup;

Improved Method II:
This is much better than Method I in efficiency, because SAS only reads in 1000 records each loop, other than reading in all the observations as in Method I. Options mprint mlogic;

 %macro subgroup;
 %local I;
 %do I=1 %to 100;
 %let A=%eval((&I-1)*1000+1);
 %let B=%eval(&I*1000);
 %put A=*&A*   B=*&B*;

 data Z&I;
 set AAA (firstobs=&A   obs=&B);
 run;
 %end;
 %mend;
 %subgroup;

Improved Method III:

 Data BBB;
 Set AAA;
 Order=_N_;
 run;

 %macro subgroup;
 %local I;
 %do I=1 %to 100;
 data Z&I (drop=Order);
 set BBB;
 where Order LE &I*1000 and Order GT (&I-1)*1000; 
 run;
 %end;
 %mend;
 %subgroup;

WHERE statement will do subsetting at compile time. This method is also more efficient than Method I. Bingo!