change data value until a certain condition is true

[JoVe]

Hi,

I'm generating samples and I'm trying to change a binary value in one particular column of the generated data. The data is sorted from large to small values in the T column and the binary values (BinT) should be 1 for values of T larger than the first T value where BinT=1. 

So, the following dataset 

Obs	Id	T	binT
1	100	46	0
2	34	39	0
3	64	38	1
4	1	36	0
5	57	36	1
6	76	34	1
7	30	32	0
8	46	32	1
9	70	32	0
10	53	30	0

should look like

Obs	Id	T	binT
1	100	46	1
2	34	39	1
3	64	38	1
4	1	36	0
5	57	36	1
6	76	34	1
7	30	32	0
8	46	32	1
9	70	32	0
10	53	30	0

I have tried several things, such as 

data want; 
_binT1=binT1; 
do until(done); 
set have;
done= (binT1=1);
if ^done then _binT1=1;
end; 
output; 
run; 

and 

data test; 
x=binT1; 
do _N_=1; 
set treat_test;
if binT1=1 then leave;
else x=1; 
end;  
run;  

but that does lead to the desired result.  

Hoping that someone can point me into the right direction.

Best. 

Jo

[Duggins · Accepted solution]

Here you go. It isn't extremely efficient, because you could theoretically have to process the entire data set twice (if your first binT=1 value is last) but for small-ish data sets it should get the job done. The idea is to first loop through the data and identify where the first binT=1 value appears. LEAVE-ing the loop immediately sets the value of i to the record where this occurs. Next, just loop through all the data and change the value of binT for those early records.

data want;
  if 0 then set have nobs = _nobs;
  do i = 1 to _nobs;
    set have point = i;
    if bint = 1 then leave;
  end;
  do j = 1 to _nobs;
    set have point = j;
    if j < i then bint = 1;
    output;
  end;
  stop;
run;

[JoVe]

Works as a charm!

Thank you dugginsj.