Join overlapping date ranges

Question

I need to join table A and table B to create table C.

Table A and Table B store status flags for the IDs. The status flags (A_Flag and B_Flag) can change from time to ti

Answer 1

One possible SAS solution to this is to perform a partial join, and then create the necessary additional rows in the data step. This should work assuming tableA has all possible records; if that's not the case (if tableB can start before tableA), some additional logic may be needed to consider that possibility (if first.id and start gt b_start). There may also be additional logic needed for issues not present in the example data - I don't have a lot of time this morning and didn't debug this for anything beyond the example data cases, but the concept should be evident.

data tableA;
informat start end DDMMYY10.;
format start end DATE9.;
input ID  Start           End     A_Flag;
datalines;
1   01/01/2008  23/03/2008  1
1   23/03/2008  15/06/2008  0
1   15/06/2008  18/08/2008  1
;;;;
run;

data tableB;
informat start end DDMMYY10.;
format start end DATE9.;
input ID  Start           End     B_Flag;
datalines;
1   19/01/2008  17/02/2008  1
1   17/02/2008  15/06/2008  0
1   15/06/2008  18/08/2008  1
;;;;
run;


proc sql;
create table c_temp as 
    select * from tableA A 
        left join (select id, start as b_start, end as b_end, b_flag from tableB) B
    on A.Id = B.id
    where (A.start le B.b_start and A.end gt B.b_start) or (A.start lt B.b_end and A.end ge B.b_end)
    order by A.ID, A.start, B.b_start;
quit;

data tableC;
set c_temp;
by id start;
retain b_flag_ret;
format start_fin end_fin DATE9.;
if first.id then b_flag_ret=0;
do until (start=end);
    if (start lt b_start) and first.start then do;
        start_fin=start;
        end_fin=b_start;
        a_flag_fin=a_flag;
        b_flag_fin=b_flag_ret;
        output;
        start=b_start;
    end;    
    else do; *start=b_start;
            start_fin=ifn(start ge b_start, start, b_start);
            end_fin = ifn(b_end le end, b_end, end);
            a_flag_fin=a_flag;
            b_flag_fin=b_flag;
            output;
            start=end; *leave the loop as there will be a later row that matches;
    end;
end;
run;