SAS Helpful Hints

Carrying forward data(Retain)

To carry data from one observation to the next, values must be retained.

* Sort the data appropriatly;
Proc Sort Data=work.A; By id visit; Run;

Data work.B;
    Retain first_x;
    Set work.A;
    By id visit;
    * To ensure that we do not carry data to where it
    * does not belong, set first_x to missing;
    * Without this, a previous ID's X could be used
    * in the next ID, if visit was never equal to 1.;
    If first.id Then first_x=.;
    * Save the first x when visit=1;
    If visit=1 Then first_x=x;
    change_x=x-first_x;
Run;

Results

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