Flag next date after index date by group

[MB_Analyst]

I am trying to flag the date that is closet to the index date. My data looks like:

ID       Index        date

1           1            20MAR2020 

1           0          21MAR2020

2           1         10APR2020

2           0          13APR2020

2          0          15APR2020

I would like to flag:

ID       Index        date                     close

1           1            20MAR2020           .

1           0           21MAR2020           1

2          1          10APR2020             .

2           0         13APR2020            1

2          0          15APR2020             0

[PaigeMiller · Accepted solution]

data want;
    set have;
    prev_id=lag(id);
    prev_index=lag(index);
    if prev_id=id and prev_index=1 then close=1;
    else if prev_id=id and prev_index=0 then close=0;
run;

This assumes the data is sorted properly, and you are looking for  next date after index as your title indicates and not closest date as your text indicates.