data a; input clm clmv; cards; 0 10 100 10 200 10 300 10 600 10 400 20 500 20 1000 20 2000 20 3000 20 4000 30 5000 30 ; run; data b; value = first.clmv; set a; by clmv; value1 = first.clmv; run;     My question is: why is there a difference  when I write "first." before the set statement and after the set statement? Can anyone explain that? ... View more

data one; if _n_ = 1 then do i = 1 to 4; set sashelp.class; end; value = _n_; output; run;   I want to understand why there are two outputs. As per the logic, there should be one output, when _n_ = 2, all the column values should go missing. then why the first observation is being retained? ... View more