Assign the same number to obs within the same group

[roroholic123]

I have a dataset that is grouped by a variable 'group':

```

id group
1 a
2 a
3 a
4 b
5 b 
6 b
7 c
8 c
9 d
10 d
11 d
12 d
13 d

```

My goal is to create a serial number that assigns the same number to obs within the same group:

```

id group number
1 a 1
2 a 1
3 a 1
4 b 2
5 b 2
6 b 2
7 c 3
8 c 3
9 d 4
10 d 4 
11 d 4
12 d 4
13 d 4

```

[japelin · Accepted solution]

how about this

data have;
  input id group $;
datalines;
1 a
2 a
3 a
4 b
5 b 
6 b
7 c
8 c
9 d
10 d
11 d
12 d
13 d
;
run;
proc sort data=have;
  by id group;
run;
data want;
  set have;
  by id group;
  retain number;
  if not(group=lag(group)) then number+1;
run;

[roroholic123]

Thank you!!!