Derive Base line visit's Value

[tsureshinvites]

data sv_raw1;
input PT_ID $ Visit $ Res;
datalines;
2 4 10
2 5 15
1 1 20
1 2 40
1 3 30
2 1 30
2 2 60
2 3 50
3 1 .
3 2 40
3 3 60
3 4 70
4 1 30
4 2 20
4 3 30
4 4 35
5 1 90
5 2 91
5 3 30
5 4 40
5 5 70
6 1 .
6 2 .
6 3 30
6 4 40
1 0 10
2 0 10
3 0 10
4 0 10
5 0 10
6 0 10
;

Scenario:

1. Baseline visit = 2.

2. Prior baseline visit's res value ( 0,1) should populate  in BASE (Variable)

3. Post Baseline visit's res value (3+ visits) should populate in BASE (Variable) 

3. if Visit 2 value is missing then prior visit's value should populate in BASE (Variable) 

Output Required:

PT_ID	Visit	Res	Base
1	0	10	10
1	1	20	10
1	2	40	40
1	3	30	40
2	0	10	10
2	1	30	10
2	2	60	60
2	3	50	60
2	4	10	60
2	5	15	60
3	0	10	10
3	1	.	10
3	2	40	40
3	3	60	40
3	4	70	40
4	0	10	10
4	1	30	10
4	2	20	20
4	3	30	20
4	4	35	20
5	0	10	10
5	1	90	10
5	2	91	91
5	3	30	91
5	4	40	91
5	5	70	91
6	0	10	10
6	1	.	10
6	2	.	10
6	3	30	10
6	4	40	10

My code:

proc sort data=sv_raw1 out=sv1;
by PT_ID Visit Res;
run;

data baseline1;
set sv1;
retain Base;
by PT_ID Visit Res;
if first.PT_ID then Base = Res;
else if visit eq '2' then Base = Res;
else if visit not in ('2') then
run;

[Astounding]

Because you created VISIT as character, you could run into trouble if any of the VISIT values are greater than "9".  For example, when sorting character variables, "10" sorts before "2". 

Assuming the VISIT values are always one digit long, you could use:

data baseline1;
set sv1;
retain Base;
by PT_ID Visit Res;
if visit le '2' then Base = Res;
run;

This logic also assumes that each PT_ID has an initial VISIT with a value less than "2".