first.variable in a group

Aexor — Tue, 01 Jun 2021 19:31:59 GMT

Could you please explain below code ;

data xyz;
input x $;
cards;
AA
AA
AA
BB
BB
;
run;

data A;
set xyz;
by x;
if first.x then
N+1;
run;

output :-

Obs x N
1 AA 1
2 AA 1
3 AA 1
4 BB 2
5 BB 2

data B;
set xyz;
by x;
if first.x then N=1;
else N+1;
run;

output for B is

Obs x N
1 AA 1
2 AA 2
3 AA 3
4 BB 1
5 BB 2

I know how dateset B is created its the incrementing the value based of the occurrence of by group x but not sure how dataset A is being created .

Please explain.

Re: first.variable in a group

Kurt_Bremser — Tue, 01 Jun 2021 19:42:47 GMT

The SUM statement

N + 1;

implies an automatic RETAIN of the variable.

In dataset A, the increment happens only when a new group starts; when this happens the first time (and N is still missing), N is set to 1 (like it happens with missing values in a SUM function).

topic first.variable in a group in SAS Programming

first.variable in a group

Re: first.variable in a group