Interleaving SAS Data Sets (by common patient number)

Question

I need to interleave to SAS dataset, but only if the patient ID exist in both of them. In a merge statement I'd use "in" and "if", however, I need to stack the data. Data is equivalent in terms of variables.

Any ideas?

Answer 1

If you have duplicates per ID in one or both datasets, then you have a bunch of other solutions. This is the one most similar to your MERGE idea.

In a Double DoW loop, you loop through the datasets twice, once to check for your condition, then once to actually output. This lets you look at all rows for each ID, see if your condition is valid, then look at them all again to act on that condition.

data have_1;
  do id = 1 to 20 by 2;
    output;
    output;
  end;
run;

data have_2;
  do id = 1 to 20 by 3;
    output;
    output;
  end;
run;



data want;
  _a=0;  *initialize temporary variables;
  _b=0;  *they will be cleared once for each ID;
  do _n_ = 1 by 1 until (last.id);
    set have_1(in=a) have_2(in=b);
    by id;
    if a then _a=1;  *save that value temporarily;
    if b then _b=1;  *again temporary;
  end;
  do _n_ = 1 by 1 until (last.id);
    set have_1 have_2;
    by id;
    if _a and _b then output;  *only output the rows that have both _a and _b;
  end;
run;