Drop observations once condition is met by multiple variables - sas

Question

I have the following data and used one of the existing answered questions to solve my data problem but could not get what I want. Here is what I have in my data
Amt1 is populated when the Evt_type is Fee
Amt2 is populated when the Evt_type is REF1/REF2
I don't want to display any observations after the last Flag='Y'
If there is no Flag='Y' then I want all the observations for that id (e.g. id=102)
I want to display if the next row for that id is a Fee followed by REF1/REF2 after flag='Y' (e.g. id=101) However I don't want if there is no REF1/REF2 (e.g.id=103)
Have:
id Date Evt_Type Flag Amt1 Amt2
101 2/2/2019 Fee 5
101 2/3/2019 REF1 Y 5
101 2/4/2019 Fee 10
101 2/6/2019 REF2 Y 10
101 2/7/2019 Fee 4
101 2/8/2019 REF1
102 2/2/2019 Fee 25
102 2/2/2019 REF1 N 25
103 2/3/2019 Fee 10
103 2/4/2019 REF1 Y 10
103 2/5/2019 Fee 10
Want:
id Date Evt_Type Flag Amt1 Amt2
101 2/2/2019 Fee 5
101 2/3/2019 REF1 Y 5
101 2/4/2019 Fee 10
101 2/6/2019 REF2 Y 10
101 2/7/2019 Fee 4
101 2/8/2019 REF1
102 2/2/2019 Fee 25
102 2/2/2019 REF1 N 25
103 2/4/2019 REF1 Y 10
103 2/5/2019 Fee 10
I tried the following
data want;
set have;
by id Date;
drop count;
if (first.id or first.date) and FLAG='Y' then
do;
retain count;
count=1;
output;
return;
end;
if count=1 and ((first.id or first.date) and Flag ne 'Y') then
do;
retain count;
delete;
return;
end;
output;
run;
Any help is appreciated.
Thanks

Answer 1

A technique known as DOW loop can perform a computation that measures a group in some way and then, in a second loop, apply that computation to members of the group.
The DOW relies on a SET statement inside the loop. In this case the computation is 'what row in the group is the last one having flag="Y".
data want;
* DOW loop, contains computation;
_max_n_with_Y = 1e12;
do _n_ = 1 by 1 until (last.id);
set have;
by id;
if flag='Y' then _max_n_with_Y = _n_;
end;
* Follow up loop, applies computation;
do _n_ = 1 to _n_;
set have;
if _n_ <= _max_n_with_Y then OUTPUT;
end;
drop _:;
run;

Answer 2

Here is one way
data have;
input id $ Date : mmddyy10. Evt_Type $ Flag $ Amt1 Amt2;
format Date mmddyy10.;
infile datalines dsd missover;
datalines;
101,2/2/2019,Fee,,5,
101,2/3/2019,REF1,Y,,5
101,2/4/2019,Fee,,10,
101,2/6/2019,REF2,Y,,10
101,2/7/2019,Fee,,4,
102,2/2/2019,Fee,,25,
102,2/2/2019,REF1,N,25,
;
data want;
do _N_ = 1 by 1 until (last.id);
set have;
by id;
if flag = "Y" then _iorc_ = _N_;
end;
do _N_ = 1 to _N_;
set have;
if _N_ le _iorc_ then output;
end;
_iorc_=1e7;
run;