How to go through all IDs in a datset to flag those records that match a value in another variable

[Kc2]

Hello,

I Have a data set which has 2 Ids values: ID1 and ID2. I would like to set a flag for all the records where ID2 in ne record is ID1 in another record and vice versa.

ID1  ID2  FLAG
A       B       1
B       A       1
C      G      0
E                0
F      H       0

Any Idea ?

Thanks

KC

[novinosrin · Accepted solution]

data have;
input ID1 $ ID2 $;
cards;
A       B       1
B       A       1
C      G      0
E       .         0
F      H       0
;

proc sql;
create table want as
select a.*,(a.id1=b.id2) as Flag
from have a left join have b
on a.id1=b.id2;
quit;

[Kc2]

thank you it worked. I was thinking about a loop or an array but this is easier.