compare two numeric observations and retain the first instance

[zqkal]

I have a dataset similar to this. I want to compare fcst_val and val variables and retain the instance of desc column where the fcst_val less than or equal to the val. 
Here is an example: 

data have; 
input type $ desc $ mo fcst_val val; 
datalines; 
A D2 0 100 1000
A D1 1 100 1050
A B1 2 100 1100
B D1 0 200 150
B B0 1 200 250
B D2 2 200 300
B B1 3 200 350
c D2 0 400 10 
C D1 1 400 300
C B1 1 400 400
;
run;

data want; 
input type $ desc $ mo fcst_val val new_val; 
datalines; 
A D2 0 100 1000  D2
A D1 1 100 1050  D2    
A B1 2 100 1100  D2 
B D1 0 200 150   B0
B B0 1 200 250   B0
B D2 2 200 300   B0
B B1 3 200 350   B0
c D2 0 400 10    B1
C D1 1 400 300   B1
C B1 1 400 500   B1
;
run;

[novinosrin · Accepted solution]

Hi @zqkal 

data have; 
input type $ desc $ mo fcst_val val; 
datalines; 
A D2 0 100 1000
A D1 1 100 1050
A B1 2 100 1100
B D1 0 200 150
B B0 1 200 250
B D2 2 200 300
B B1 3 200 350
C D2 0 400 10 
C D1 1 400 300
C B1 1 400 500
;
run;

data want;
do until(last.type);
set have;
by type;
length new_val $10;
if fcst_val<val and missing(new_val) then new_val=desc;
end;
do until(last.type);
set have;
by type;
output;
end;
run;

[zqkal]

Thanks for your help