SAS find in order variables - sas

Question

I need to find who has in order A-B-C. Please check the table for example;
id term grade subj num
10 2002 D 332 1
10 2002 A 333 2
11 2005 C 232 1
11 2005 A 232 2
11 2005 B 232 3
11 2005 C 232 4
15 2010 A 130 1
15 2010 B 130 2
15 2010 C 130 3
20 2000 B 500 1
20 2000 A 500 2
20 2000 C 500 3
What i need fromthis table is id : 11 AND 15
The output should be like
id term subj
11 2005 232
15 2010 130
So i need list the id's that had Grade of 'A' in it then was changed to 'B' then it was changed to 'C' .
Num could be in order. It dosen't have to start from 1, it could be 1 or 2 or 3, etc. But it should be in order A then B then C
I dont need to see the ID=20 bec for the num order grades' are not in order.

Answer 1

If all you are looking for is a simple 'A'-'B'-'C' sequence, then the LAG() function is sufficient. That is what I show in the example below. If you are looking for more sequences (e.g. 'A'-'B', 'B'-'C', 'A'-'B'-'C'-'D'), a slightly more complex solution is needed. If so, I'll edit the answer accordingly.
Below is a test program showing the implementation:
DATA d1;
INPUT
id :8.
term :8.
grade :$2.
subj :8.
num :8.
;
DATALINES;
10 2002 D 332 1
10 2002 A 333 2
11 2005 C 232 1
11 2005 A 232 2
11 2005 B 232 3
11 2005 C 232 4
15 2010 A 130 1
15 2010 B 130 2
15 2010 C 130 3
;
RUN;
DATA d2 (
KEEP = id term subj
);
SET d1;
grade_previous_1 = LAG1(grade);
grade_previous_2 = LAG2(grade);
IF (grade = 'C' AND grade_previous_1 = 'B' AND grade_previous_2 = 'A');
RUN;
Note that the LAG functions must be evaluated on their own lines and stored in variables, as shown above - don't fold them into the IF conditions or they won't always get executed. That is, don't say:
IF (grade = 'C' AND LAG1(grade) = 'B' AND LAG2(grade) = 'A');
That actually works in this example but in general it's better to get into the habit of calling LAG() outside of IF conditions and storing results in temporary variables.