/*导入数据*/
data a;
input group $ indexyear Pair_ID;
cards;
case 2011 0000048810
control 2009 0000048810
control 2006 0000048810
control 2007 0000145478
control 2010 0000145478
case 2013 0000145478
case 2010 0000151800
control 2013 0000151800
control 2007 0000151800
control 2010 0000151800
control 2012 0000151800
control 2011 0000151800
;
run;
/*把case 和 control 的数据分开，再横向连接，方便计算最接近的年份，也就是年作差的绝对值。*/
/*                数据分开*/
data a_case  a_control;
set a;
if group="case" then output a_case;
if group="control" then output a_control;
run;
/*                排序*/
proc sort data=a_case out=a_case2(rename=(indexyear=case_year));
by pair_id ;
run;
/*                排序*/
proc sort data=a_control out=a_control2(rename=(indexyear=control_year));
by pair_id descending indexyear ;
run;
/*                横向合并*/
data a_merge;
merge a_case2 a_control2;
by pair_id;
run;
/*                作差*/
data a_merge2;
   set a_merge;
        yeardif=min(abs(control_year-case_year));
        run;
/*                按pair_id yeardif分组排序，*/
proc sort data=a_merge2;
by pair_id yeardif;
run;
/*排序后，取相同pair_id的第yeardif一条，也就是最接近case年份那条*/
data a_end;
        set a_merge2;
        by pair_id yeardif;
        if first.pair_id;
        run;

proc sql;
create table selection as
select control.*,
abs(control.indexyear-case.year) as diff,
min(calculated diff) as min
from (select *
       from A
       where group="control") control
left join (select indexyear as year,
                    Pair_ID as ID
             from A
             where group="case") case
on control.Pair_ID=case.ID
group by Pair_ID;
quit;

proc sql;
create table want as
select group,
       indexyear,
       Pair_ID
from selection
where diff=min;
quit;