flag record has same date

[jojozheng]

I have a dataset below:

date     id    first

MAY     1     1

MAY     1      

JUN      1         

SEP     2     1

SEP     2       

I want record with same date to mark as first=1, like

date     id    first

MAY     1     1

MAY     1      1

JUN      1         

SEP     2     1

SEP     2     1

group by id date. 

cannot use retain, cause it failed as 

date     id    first

MAY     1     1

MAY     1      1

JUN      1    1        -----------I don't want JUN to be as first=1, I just want all same date MAY to be first=1. 

[ChrisNZ]

Why did you start a new thread?

What's wrong with the one you created here?

Did you try all the solutions given (including @Astounding's?

If you did, explain why they don't suit.

And of course, clearly provide the expected output.

[Jagadishkatam]

data have;
input date :$3.    id    first;
cards;
MAY     1     1
MAY     1     . 
JUN      1    .     
SEP     2     1
SEP     2     .  
;

proc sort data=have;
by date;
run;


data want;
do until(last.date);
set have;
by date;
retain cnt;
if first.date then cnt=1;
else cnt+1;
end;
do until(last.date);
set have;
by date;
if cnt>1 then flag=1;
else flag=.;
output;
end;
run;

[Reeza · Accepted solution]

What about September?

You're correct that RETAIN may not work - and it likely own't with a variable already present. But if you create a new variable and work with that it will work fine. 

data have;
    input date :$3. id first;
    cards;
MAY     1     1
MAY     1     . 
JUN      1    .     
SEP     2     1
SEP     2     .  
;

data temp;
    set have;
    by date notsorted;
    retain flag;

    if first.date and first=1 then
        flag=1;
    else if first.date then
        call missing(flag);
run;

data want;
    set temp;
    where flag=1;
run;

---

@jojozheng wrote:

I have a dataset below:

date     id    first

MAY     1     1

MAY     1      

JUN      1         

SEP     2     1

SEP     2       

I want record with same date to mark as first=1, like

date     id    first

MAY     1     1

MAY     1      1

JUN      1         

SEP     2     1

SEP     2     1

group by id date. 

cannot use retain, cause it failed as 

date     id    first

MAY     1     1

MAY     1      1

JUN      1    1        -----------I don't want JUN to be as first=1, I just want all same date MAY to be first=1. 

---