count variable with condition and assign to the max value

[CHL0320]

Hi

I have a SAS question and would like to have your help.  I need to create a count variable when the day variable is in (1,6,7) per ID, and then assign that count variable to the max value. The order cannot be changed. For example

Data have: ID, day

A   7

A   4

A   5

B   4

B   1

B   7

B   3

C   7

C   1

C   2

D   2

D   3

D   7

E   1

E   2

E   3

E   4

Data  want is: ID, day, N_day

A   7   1

A   4   1

A   5   1

B   4   2 

B   1   2

B   7   2

B   3   2

C   7   3

C   1   3

C   6   3

D   2   1

D   3   1

D   7   1

E   2   0

E   2   0

E   3   0

E   4   0

Thank you for your help.

[34reqrwe]

Why does the count increase by 1 at this line?

B   4   2 

[PeterClemmensen · Accepted solution]

Your day variable is not the same in your two data sets.

Anyway, you can do like this

data have;
input id $ day;
datalines;
A   7
A   4
A   5
B   4
B   1
B   7
B   3
C   7
C   1
C   6
D   2
D   3
D   7
E   2
E   2
E   3
E   4
;

data want;
   N_day=0;
   do until (last.id);
      set have;
      by id;
      if day in (1, 6, 7) then N_day=N_day+1;
   end;
   do until (last.id);
      set have;
      by id;
      output;
   end;
run;