how to replace missing value by last value

[alepage]

When flag is equal to one how to replace missing value by 20230127 ?

data test;
input flag $ date $;
datalines;
0 20250128
0 20250128
0 20250127
0 20250127
0 20250127
0 20250127
0 20250127
1 .
1 .
1 .
1 .
1 .
1 .
1 .
1 .
1 .
1 .
0 20250124
0 20250124
0 20250124
0 20250124
0 20250124
;
run;

[ballardw · Accepted solution]

To replace "by last value", which is NOT 20230127 in your example data set:

data want;
  set test;
  length d $ 8;
  retain d;
  if not missing(date) then d=date;
  if flag='1' then date=d;
run;

Retain keeps the value of a variable across data step boundaries. So create a new variable to hold the value with retain when assigned and then use the value as needed.

Anything called a "date" that is character is asking for all sorts of difficulty in working with.