Test if a variable exists

Question

I want to test if a variable exists and if it doesn't, create it.

Answer 1

The open()&varnum() functions can be used. Non-zero output from varnum() indicates the variable exists.

data try; 
    input var1 var2 var3;
    datalines;
    7 2 2
    5 5 3
    7 2 7
; 

data try2; 
    set try;
    if _n_ = 1 then do; 
        dsid=open('try'); 
        if varnum(dsid,'var4') = 0 then var4 = .; 
        rc=close(dsid);
    end;
    drop rc dsid;    
run;

Answer 2

data try2;
    set try;
    var4 = coalesce(var4,.);
run;

(assuming var4 is numeric)