Hello Experts,   My data is :  data donnees; input ID X2 X3; cards; 1 10 20 2 38 50 3 45 60 4 70 80 ; run; I would like to calculate my values with lag from the line _N_-1, but this lags is also calculated. My code is :  data donnees1; set donnees; /**Calculation of X4 and X5***/ if ID=1 then do; X4=.; X5=X3; end; X5_avant=lag(X5); if ID=2 then do; X4=X5_avant+X2; X5=X5_avant+X3; end; X5_avant=lag(X5); if ID=3 then do; X4=X5_avant+X2; X5=X5_avant+X3; end; X5_avant=lag(X5); if ID=4 then do; X4=X5_avant+X2; X5=X5_avant+X3; end; run; I wrote a macro where I recreate the data: /****Solution***/ %macro values; %do i=1 %to 3; data donnees; set donnees; /**Calculation of X4 and X5***/ if ID=1 then do; X4=.; X5=X3; end; X5_avant=lag(X5); if ID^=1 then do; X4=X5_avant+X2; X5=X5_avant+X3; end; X5_avant=lag(X5); run; %end; %mend; %values; Do you know please another more efficient algorithme that takes less time ?   Thank you very much !   ... View more