坐等

data test;
    input class $ year;
cards;
a 2001
a 2002
a 2003
a 2005
a 2007
a 2008
a 2009
a 2010
b 2001
b 2003
b 2004
b 2005
b 2009
;
run;

proc sort data=test;
    by class year;
run;

data test1;
    set test;
    by class year;
    year_lag=lag(year);
    last+1;
    if year-year_lag>1 or first.class then last=1;
run;

        

感谢！