How to put duplicates into different groups based on the original order?

[SAS-questioner]

Hi, I have a question about how to put duplicates into different groups based on the original order? I have a data like below:

ID  condition
1        A
1        A
2        B
2        B
3        A
3        A
3        B
3        B
4        B
4        B
4        A
4        A
5        A
5        A
5       B
5       B
5       A
5       A       

The data is like above, basically, there are five situations: 1. all As; 2, all Bs; 3, A first and then B; 4, B first and then A; 5, A first and then B, and then A.

I want to keep the original order, which means I can't use proc sort, because after I use proc sort, AABBAA or BBAA will become AAAABB and AABB.

What I want to do is to put ID with all As in group 1, put ID with all Bs in group 2, and put ID with A first and then B in to group 3. So, for the rest of patterns like B first and then A, or A first and then B, and then A can be removed. I am wondering if there is a way to do it? Hopefully that I express myself clearly. Thank you!

[Tom · Accepted solution]

If you just want those specific groups AB, BA, A , B and perhaps none then you could do something like this:

data want;
  do row=1 by 1 until (last.id);
    set have;
    by id;
    if condition='A' then a=min(a,row);
    else if condition='B' then b=min(b,row);
  end;
  length group $2 ;
  if . < a < b then group='AB';
  else if . < b < a then group='BA';
  else if . < b then group='B';
  else if . < a then group='A';
  keep id group;
run;

Result

Obs    ID    group

 1     1      A
 2     2      B
 3     3      AB
 4     4      BA
 5     5      AB

If you also want to look for longer patterns, like ABA you might use something like:

data want;
  set have;
  by id condition notsorted;
  length group $8 ;
  retain group;
  if first.id then group=' ';
  if first.condition then group=cats(group,condition);
  if last.id;
  keep id group;
run;

Result

Obs    ID    group

 1     1      A
 2     2      B
 3     3      AB
 4     4      BA
 5     5      ABA

[SAS-questioner]

Work like charm! Thank you!