1. Dr. Arthur Tabachneck Director, Data Management
Look Both Ways
Dr. Arthur Tabachneck Director, Data Management
Note: program stolen from a SASOPEDIA article by Howard Schreier

2. suppose you had the following data:
data have;
input ID $ Measure;
cards;
A 11
A 12
A 13
A 14
B 21
B 22
B 23 ;

3. and you needed to have the following table:
data need;
input ID $ Measure Next_Measure Last_Measure;
cards; A A A A B B B ;

4. that is, with the following assignments made:
ID Measure Next_Measure Last_Measure A A A A B B B

5. that is, with the following assignments made:
ID Measure Next_Measure Last_Measure A A A A B B B

6. that is, with the following assignments made:
ID Measure Next_Measure Last_Measure A A A A B B B

7. a data step solution data need; set have; by ID;
set have ( firstobs = 2 keep = Measure
rename = (Measure = Next_Measure) )
have ( obs = 1 drop = _all_);
Last_Measure = ifn( first.ID, (.), lag(Measure) );
Next_Measure = ifn( last.ID, (.), Next_Measure );
run;

8. Why it works: Under the hood-Iteration #1:
ID Measure FIRST.ID LAST.ID Next_Measure Last_Measure _ERROR_ _N_ A
PDV
ID Measure A A A A B B B
data need;
set have;
by ID;
PutLog _all_ ;
set have ( firstobs = 2 keep = Measure
rename = (Measure = Next_Measure) )
have ( obs = 1 drop = _all_);
Last_Measure = ifn( first.ID, (.), lag(Measure) );
Next_Measure = ifn( last.ID, (.), Next_Measure );
run;

9. Why it works: Under the hood-Iteration #1:
ID Measure FIRST.ID LAST.ID Next_Measure Last_Measure _ERROR_ _N_ A
PDV
ID Measure A A A A B B B
data need;
set have;
by ID;
PutLog _all_ ;
set have ( firstobs = 2 keep = Measure
rename = (Measure = Next_Measure) )
have ( obs = 1 drop = _all_);
Last_Measure = ifn( first.ID, (.), lag(Measure) );
Next_Measure = ifn( last.ID, (.), Next_Measure );
run;

10. Why it works: Under the hood-Iteration #1:
ID Measure FIRST.ID LAST.ID Next_Measure Last_Measure _ERROR_ _N_ A
PDV
ID Measure A A A A B B B
data need;
set have;
by ID;
PutLog _all_ ;
set have ( firstobs = 2 keep = Measure
rename = (Measure = Next_Measure) )
have ( obs = 1 drop = _all_);
Last_Measure = ifn( first.ID, (.), lag(Measure) );
Next_Measure = ifn( last.ID, (.), Next_Measure );
run;

11. Why it works: Under the hood-Iteration #2:
ID Measure FIRST.ID LAST.ID Next_Measure Last_Measure _ERROR_ _N_ A
PDV
ID Measure A A A A B B B
data need;
set have;
by ID;
PutLog _all_ ;
set have ( firstobs = 2 keep = Measure
rename = (Measure = Next_Measure) )
have ( obs = 1 drop = _all_);
Last_Measure = ifn( first.ID, (.), lag(Measure) );
Next_Measure = ifn( last.ID, (.), Next_Measure );
run;

12. Why it works: Under the hood-Iteration #2:
ID Measure FIRST.ID LAST.ID Next_Measure Last_Measure _ERROR_ _N_ A
PDV
ID Measure A A A A B B B
data need;
set have;
by ID;
PutLog _all_ ;
set have ( firstobs = 2 keep = Measure
rename = (Measure = Next_Measure) )
have ( obs = 1 drop = _all_);
Last_Measure = ifn( first.ID, (.), lag(Measure) );
Next_Measure = ifn( last.ID, (.), Next_Measure );
run;

13. Why it works: Under the hood-Iteration #2:
ID Measure FIRST.ID LAST.ID Next_Measure Last_Measure _ERROR_ _N_ A
PDV
ID Measure A A A A B B B
data need;
set have;
by ID;
PutLog _all_ ;
set have ( firstobs = 2 keep = Measure
rename = (Measure = Next_Measure) )
have ( obs = 1 drop = _all_);
Last_Measure = ifn( first.ID, (.), lag(Measure) );
Next_Measure = ifn( last.ID, (.), Next_Measure );
run;

14. Why it works: Under the hood-Iteration #3:
ID Measure FIRST.ID LAST.ID Next_Measure Last_Measure _ERROR_ _N_ A
PDV
ID Measure A A A A B B B
data need;
set have;
by ID;
PutLog _all_ ;
set have ( firstobs = 2 keep = Measure
rename = (Measure = Next_Measure) )
have ( obs = 1 drop = _all_);
Last_Measure = ifn( first.ID, (.), lag(Measure) );
Next_Measure = ifn( last.ID, (.), Next_Measure );
run;

15. Why it works: Under the hood-Iteration #3:
ID Measure FIRST.ID LAST.ID Next_Measure Last_Measure _ERROR_ _N_ A
PDV
ID Measure A A A A B B B
data need;
set have;
by ID;
PutLog _all_ ;
set have ( firstobs = 2 keep = Measure
rename = (Measure = Next_Measure) )
have ( obs = 1 drop = _all_);
Last_Measure = ifn( first.ID, (.), lag(Measure) );
Next_Measure = ifn( last.ID, (.), Next_Measure );
run;

16. Why it works: Under the hood-Iteration #3:
ID Measure FIRST.ID LAST.ID Next_Measure Last_Measure _ERROR_ _N_ A
PDV
ID Measure A A A A B B B
data need;
set have;
by ID;
PutLog _all_ ;
set have ( firstobs = 2 keep = Measure
rename = (Measure = Next_Measure) )
have ( obs = 1 drop = _all_);
Last_Measure = ifn( first.ID, (.), lag(Measure) );
Next_Measure = ifn( last.ID, (.), Next_Measure );
run;

17. Why it works: Under the hood-Iteration #4:
ID Measure FIRST.ID LAST.ID Next_Measure Last_Measure _ERROR_ _N_ A
PDV
ID Measure A A A A B B B
data need;
set have;
by ID;
PutLog _all_ ;
set have ( firstobs = 2 keep = Measure
rename = (Measure = Next_Measure) )
have ( obs = 1 drop = _all_);
Last_Measure = ifn( first.ID, (.), lag(Measure) );
Next_Measure = ifn( last.ID, (.), Next_Measure );
run;

18. Why it works: Under the hood-Iteration #4:
ID Measure FIRST.ID LAST.ID Next_Measure Last_Measure _ERROR_ _N_ A
PDV
ID Measure A A A A B B B
data need;
set have;
by ID;
PutLog _all_ ;
set have ( firstobs = 2 keep = Measure
rename = (Measure = Next_Measure) )
have ( obs = 1 drop = _all_);
Last_Measure = ifn( first.ID, (.), lag(Measure) );
Next_Measure = ifn( last.ID, (.), Next_Measure );
run;

19. Why it works: Under the hood-Iteration #4:
ID Measure FIRST.ID LAST.ID Next_Measure Last_Measure _ERROR_ _N_ A
PDV
ID Measure A A A A B B B
data need;
set have;
by ID;
PutLog _all_ ;
set have ( firstobs = 2 keep = Measure
rename = (Measure = Next_Measure) )
have ( obs = 1 drop = _all_);
Last_Measure = ifn( first.ID, (.), lag(Measure) );
Next_Measure = ifn( last.ID, (.), Next_Measure );
run;

20. Why it works: Under the hood-Iteration #5:
ID Measure FIRST.ID LAST.ID Next_Measure Last_Measure _ERROR_ _N_ B
PDV
ID Measure A A A A B B B
data need;
set have;
by ID;
PutLog _all_ ;
set have ( firstobs = 2 keep = Measure
rename = (Measure = Next_Measure) )
have ( obs = 1 drop = _all_);
Last_Measure = ifn( first.ID, (.), lag(Measure) );
Next_Measure = ifn( last.ID, (.), Next_Measure );
run;

21. Why it works: Under the hood-Iteration #5:
ID Measure FIRST.ID LAST.ID Next_Measure Last_Measure _ERROR_ _N_ B
PDV
ID Measure A A A A B B B
data need;
set have;
by ID;
PutLog _all_ ;
set have ( firstobs = 2 keep = Measure
rename = (Measure = Next_Measure) )
have ( obs = 1 drop = _all_);
Last_Measure = ifn( first.ID, (.), lag(Measure) );
Next_Measure = ifn( last.ID, (.), Next_Measure );
run;

22. Why it works: Under the hood-Iteration #5:
ID Measure FIRST.ID LAST.ID Next_Measure Last_Measure _ERROR_ _N_ B
PDV
ID Measure A A A A B B B
data need;
set have;
by ID;
PutLog _all_ ;
set have ( firstobs = 2 keep = Measure
rename = (Measure = Next_Measure) )
have ( obs = 1 drop = _all_);
Last_Measure = ifn( first.ID, (.), lag(Measure) );
Next_Measure = ifn( last.ID, (.), Next_Measure );
run;

23. Why it works: Under the hood-Iteration #6:
ID Measure FIRST.ID LAST.ID Next_Measure Last_Measure _ERROR_ _N_ B
PDV
ID Measure A A A A B B B
data need;
set have;
by ID;
PutLog _all_ ;
set have ( firstobs = 2 keep = Measure
rename = (Measure = Next_Measure) )
have ( obs = 1 drop = _all_);
Last_Measure = ifn( first.ID, (.), lag(Measure) );
Next_Measure = ifn( last.ID, (.), Next_Measure );
run;

24. Why it works: Under the hood-Iteration #6:
ID Measure FIRST.ID LAST.ID Next_Measure Last_Measure _ERROR_ _N_ B
PDV
ID Measure A A A A B B B
data need;
set have;
by ID;
PutLog _all_ ;
set have ( firstobs = 2 keep = Measure
rename = (Measure = Next_Measure) )
have ( obs = 1 drop = _all_);
Last_Measure = ifn( first.ID, (.), lag(Measure) );
Next_Measure = ifn( last.ID, (.), Next_Measure );
run;

25. Why it works: Under the hood-Iteration #6:
ID Measure FIRST.ID LAST.ID Next_Measure Last_Measure _ERROR_ _N_ B
PDV
ID Measure A A A A B B B
data need;
set have;
by ID;
PutLog _all_ ;
set have ( firstobs = 2 keep = Measure
rename = (Measure = Next_Measure) )
have ( obs = 1 drop = _all_);
Last_Measure = ifn( first.ID, (.), lag(Measure) );
Next_Measure = ifn( last.ID, (.), Next_Measure );
run;

26. Why it works: Under the hood-Iteration #7:
ID Measure FIRST.ID LAST.ID Next_Measure Last_Measure _ERROR_ _N_ B
PDV
ID Measure A A A A B B B
data need;
set have;
by ID;
PutLog _all_ ;
set have ( firstobs = 2 keep = Measure
rename = (Measure = Next_Measure) )
have ( obs = 1 drop = _all_);
Last_Measure = ifn( first.ID, (.), lag(Measure) );
Next_Measure = ifn( last.ID, (.), Next_Measure );
run;

27. Why it works: Under the hood-Iteration #7:
ID Measure FIRST.ID LAST.ID Next_Measure Last_Measure _ERROR_ _N_ B
PDV
ID Measure A A A A B B B
data need;
set have;
by ID;
PutLog _all_ ;
set have ( firstobs = 2 keep = Measure
rename = (Measure = Next_Measure) )
have ( obs = 1 drop = _all_);
Last_Measure = ifn( first.ID, (.), lag(Measure) );
Next_Measure = ifn( last.ID, (.), Next_Measure );
run;

28. Why it works: Under the hood-Iteration #7:
ID Measure FIRST.ID LAST.ID Next_Measure Last_Measure _ERROR_ _N_ B
PDV
ID Measure A A A A B B B
data need;
set have;
by ID;
PutLog _all_ ;
set have ( firstobs = 2 keep = Measure
rename = (Measure = Next_Measure) )
have ( obs = 1 drop = _all_);
Last_Measure = ifn( first.ID, (.), lag(Measure) );
Next_Measure = ifn( last.ID, (.), Next_Measure );
run;

29. ending up with the following table
ID Measure Next_Measure Last_Measure A A A A B B B

30. Questions? Your comments and questions are valued and encouraged.
Contact the author:
Dr. Arthur Tabachneck
Director, Data Management
Insurance Bureau of Canada
Toronto, Ontario L3T 5K9