data bill; input bill1 FLT fdaas billing; cards; 97975800 33614638 33614638 23377506 97975800 33614638 33614638 23377506 97988982 . . 23377506 98028109 . . 23377506 ; run; data b; set bill; retain x y; if not missing(flt) then x=flt; else flt=x; if not missing(fdaas) then y=fdaas; else fdaas=y; drop x y; run;
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