FWD> help in modifying obs To <SAS-L@VM.MARIST.EDU>

>I have two num. variables ("type" and "key"). Type takes values (1, 2, or 3) >while "key" takes values (7, 8, 9, 2 ...). What I want to do is:

>If for observation i, key=3, then for the immediately preceding observation >(i-1), I want the key value to become the value of key(i).

To obtain the preceding value of a variable you would want to use the LAG function. I would suggest taking the lag of the variable regardless of the value of type. Using IF subsetting tends to cause problems when using lag since what happens is you get the previous value of KEY that has a TYPE = 3. So, take the lag of key (lagkey=lag(key)), THEN only read the observations that have a value of 3 for type. Hope this helps!

Fran