ID # amt interval
A01 1 500 0
A01 2 2000 1500
A01 3 2200 200
如何sas计算出interval?
我尝试用retain,可是失败
data aa1;
set aa;
by ID;
retain interval;
if first.ID then do;
interval=0;
end;
interval=amt-interval;
run;
出来是:
interval
500 (i.e. amt1)
1500 (i.e. 2000-500, right)
700 (i.e. 2200-1500)
请教高手指正和支招啊~~



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