topic why the answer is 8 ? in SAS Procedures

why the answer is 8 ?

tianerhu — Sat, 01 Oct 2022 16:10:53 GMT

data work.numbers;
infile datalines;
input T;
datalines;
6
7
8
;
proc print data = work.numbers noobs;
run;

title 'sum of lag';
data work.move;
  set work.numbers;
  if _N_= 3 then total=sum(T,lag1(T),lag2(T));
run;
proc print data = work.move noobs;
run;

Re: why the answer is 8 ?

Kurt_Bremser — Sat, 01 Oct 2022 16:16:16 GMT

Because you commit the #1 capital sin of LAG: using the function conditionally. The LAG functions will only populate their queue when actually called, so you put nothing into the queue until the third observation, where the result is still missing.

Re: why the answer is 8 ?

tianerhu — Sat, 01 Oct 2022 16:31:40 GMT

Thank you for your help.

Re: why the answer is 8 ?

Tom — Sun, 02 Oct 2022 14:24:18 GMT

Looks like you want this program instead.

data work.numbers;
  input T;
datalines;
6
7
8
;
data work.move;
  set work.numbers;
  total=sum(T,lag1(T),lag2(T));
  if _N_< 3 then call missing(total);
run;