自顶。。。

PROC IMPORT OUT= a
            DATAFILE= "Y:\test.xls"
            DBMS=EXCEL REPLACE;
     SHEET="Sheet1$";
     GETNAMES=YES;

RUN;

/*Sheet1$  value as follow:
id date
cards;
1 10
2 20
3 30
4 40
5 50
;
*/


data b;
set a;
by id;
bb=lag(date);

if nmiss(bb ,date)=0 then diff=date-bb;
cc=lag(diff);

if nmiss(cc ,diff)=0 then diff2=diff-cc;

if diff2 not in (. 0) then put 'The sample is not UD'     date=;

run;