Create values for group - SAS - sas

Question

data test;
input Index Indicator value FinalValue;
datalines;
1 0 5 21
1 1 21 21
2 1 0 0
3 0 4 7
3 1 7 7
3 0 8 7
3 0 2 7
4 1 1 1
4 0 4 1
;
run;
I have a data set with the first 3 columns. How do I get the 4th columns based on the indicators? For example, for the index, when the indicator =1, the value is 21, so I put 21 is the final values in all lines for index 1.

Answer 1

Use the SAS Retain Keyword.
You can do this in a data step; by Retaining the Value where indicator = 1.
Steps:
Sort your data by Index and Indicator
Group by the Index & Retain the Value where Indicator=1
Code:
/*Sort Data by Index and Indicator & remove the hardcodeed finalvalue*/
proc sort data=test (keep= Index Indicator value);
by index descending indicator ;
run;
/*Retain the FinalValue*/
data want;
set test;
retain FinalValue;
keep Index Indicator value FinalValue;
if indicator =1 then do;FinalValue=value;end;
/*The If statement below will assign . to records that doesn't have an indicator value of 1*/
if indicator ne 1 and FIRST.Index=1 then FinalValue=.;
by index;
run;
Output:
Index=1 Indicator=1 value=21 FinalValue=21
Index=1 Indicator=0 value=5 FinalValue=21
Index=2 Indicator=1 value=0 FinalValue=0
Index=3 Indicator=1 value=7 FinalValue=7
Index=3 Indicator=0 value=4 FinalValue=7
Index=3 Indicator=0 value=8 FinalValue=7
Index=3 Indicator=0 value=2 FinalValue=7
Index=4 Indicator=1 value=1 FinalValue=1
Index=4 Indicator=0 value=4 FinalValue=1

Answer 2

Use proc sql by left join. Select value which indicator=1 and group by index, then left join with original dataset. It seemed that your first row of index=3 should be 7, not 0.
proc sql;
select a.*,b.finalvalue from test a
left join (select *,value as finalvalue from test group by index having indicator=1) b
on a.index=b.index;
quit;

Answer 3

This is rather old school but should be adequate. I reckon you call it a self merge or something.
data test;
input Index Indicator value;* FinalValue;
datalines;
1 0 5 21
1 1 21 21
2 1 0 0
3 0 4 7
3 1 7 7
3 0 8 7
3 0 2 7
4 1 1 1
4 0 4 1
;;;;
run;
data final;
if 0 then set test;
merge test(where=(indicator eq 1) rename=(value=FinalValue)) test;
by index;
run;
proc print;
run;
Final
Obs Index Indicator value Value
1 1 0 5 21
2 1 1 21 21
3 2 1 0 0
4 3 0 4 7
5 3 1 7 7
6 3 0 8 7
7 3 0 2 7
8 4 1 1 1
9 4 0 4 1