Lag Function behavior problem

[Greek]

Hello,

I am using the lag function which works for parts of my data set, while it doesn't in other parts (?) I am using this very simple data step below: Does anybody know what's wrong with this code?

Thank you!

data adjustment3;
set adjustment3;
if count_cluster=lag1(count_cluster) then Max_Salary_previous_grade=lag1(max_salary); else Max_Salary_previous_grade=0;

run;

		TABLE GET
count_cluster	Max_salary	Max_Salary_previous_grade
1	56,768	-
1	70,741	56,768	ok!
2	49,957	-
3	50,000	-
4	34,360	-
4	49,790	70,741	Error!
4	53,220	49,790	ok!
		TABLE WANT
count_cluster	Max_salary	Max_Salary_previous_grade
1	56,768	-
1	70,741	56,768
2	49,957	-
3	50,000	-
4	34,360	-
4	49,790	34,360
4	53,220	49,790

[BrunoMueller]

You can not execute the LAG function conditionally. The LAG function has to be executed for every observation.

See the sample below with the modfied logic. You can make use of BY group processing and the FIRST. functionality.

data have;
  infile cards dlm=",";
  input
    count_cluster
    Max_salary
  ;
cards;
1, 56768
1,70741
2,49957
3,50000
4,34360
4,49790
4,53220
;

data want;
  set have;
  by count_cluster;
    _prev_salary = lag1(max_salary);
  if first.count_cluster = 0 then do;
    Max_Salary_previous_grade = _prev_salary;
  end;
  drop _prev_salary;
run;

Bruno