How the variable a1 is created?

[rajeshalwayswel]

Can someone please explain how the variable a1 is created with the highlighted values?


data l l1;
set sashelp.class;
proc sort data=l;by age;
proc sort data=l1;by age;
run;


data a1;
set l(in=a obs=5) l1(in=b obs=5);
by age;
a1+b;
run;

[PGStats · Accepted solution]

variable a1 is involved in a sum statement which implies that it has initial value zero and is retained over the datastep iterations.

Each age is read in turn from (identical) datasets l and l1.

variable b is equal to 1 when reading from l1.

the sum statement a1+b; thus increments variable a1 by one each time an observation is read from dataset l1.