How to find the previous value of a variable in SAS

lag, sas

Solution

You could try using the retain statement as follows (untested):

data table2;
  set table1;

  retain prv_value .;

  if number=. then
    number=prv_value;

  if number ne . then
    prv_value=number;
run;

Problem

I am trying to populate a variable with set conditions. If the variable NUMBER is equal to . then make it equal to the previous value of Number. ``` data table2; set table1; prv_value = lag(number); if number = . then number = prv_value; run; ``` However, if there are two values in a row where number = . then the second occurrence of the value of . has it's previous value of number = . . What I would like is to find the first previous occurrence where number is not equal to . and make the value of number equal to that previous non-missing value. An example of my data is: ``` id number d10 2 d10 2 d10 3 d10 . d10 . ``` Applying the above code I would then get: ``` id number prv_number d10 2 . d10 2 2 d10 3 2 d10 3 3 d10 . . ``` What I would like is: ``` id number prv_number d10 2 . d10 2 2 d10 3 2 d10 3 3 d10 3 . ``` i.e. if number has a value of . then make it equal to the first previous occurrence of a non-missing value. In some cases in my dataset I might have: ``` id number d10 4 d10 2 d10 . d10 . d10 . d10 . ``` and what I would like is: ``` id number d10 4 d10 2 d10 2 d10 2 d10 2 d10 2 ``` (Note, my data is sorted in order of events/time, hence wanting the first previous occurence). Is there anything I can do with the lag function over different number of previous occurrences, or anything else that can do what I'd like?

Original source