Create an indicator conditional on change of values within subjects

[Dinurik]

Hi SAS programmers,

Could you please help me with this problem? I don't even know where to start learning how to do this and not sure whether it is possible.

This is the data:

    data a;
    input id time therapy;
    cards;
        1 1 0
        1 2 0
        1 3 1
        1 4 1
        2 1 2
        2 2 2
        2 3 2
        2 4 0
        3 1 1
        3 2 1
        3 3 0
        3 4 1
        4 1 1
        4  2 1
        4 3 1
        4 4 1
        ;
    run;

I need to create a time-independent indicator variable that takes the value of 1 if subject's therapy became 0 after being 1, or 2; and 0 otherwise. So, suppose therapy=0 means no therapy, while therapies 1 and 2 are types of therapy. If 0 precedes 1 or 2, it is considered it to be normal, while if it follows 1 or 2, it means discontinuation of therapy, which required attention. I ultimately need to know how many people discontinued therapy. Is it at all possible to do in SAS?

Thank you!

[novinosrin]

Hi @Dinurik  Can you please post your expected output for the input sample you posted. This can help avoid readers in assuming things that may be inaccurate. Thank you!

[Dinurik]

Yes, sorry I haven't done that. Here is the print out of the dataset i need. Discont is the new variable. 

  id    time  therapy discont

1	1	0	0
1	2	0	0
1	3	1	0
1	4	1	0
2	1	2	1
2	2	2	1
2	3	2	1
2	4	0	1
3	1	1	1
3	2	1	1
3	3	0	1
3	4	1	1
4	1	1	0
4	2	1	0
4	3	1	0
4	4	1	0

[novinosrin · Accepted solution]

Hi @Dinurik  Thank you. Please try -

 data a;
    input id time therapy;
    cards;
        1 1 0
        1 2 0
        1 3 1
        1 4 1
        2 1 2
        2 2 2
        2 3 2
        2 4 0
        3 1 1
        3 2 1
        3 3 0
        3 4 1
        4 1 1
        4  2 1
        4 3 1
        4 4 1
        ;
    run;


data discontinued_therapy;
 do _n_=1 by 1 until(last.id);
  set a;
  by id;
  if not therapy and not first.id and lag(therapy) then discont=1;
 end;
 do _n_=1 to _n_;
  set a;
  discont=^^discont;
  output;
 end;
run;

[Dinurik]

Hi @novinosrin,

Thank you so much! I wrote my one extremely inefficient code involving  proc expand to compute the lagged therapy, and creating too many intermediate variables. It was so long and ugly that I didn't dare to share it. Thank you for this short and elegant beauty! Could you please refer me to any education materials where I could educate myself on this kind of programming in SAS? 

Thanks again!

[novinosrin]

The following books are very useful and helped me along the way in my SAS journey so far-

1. Learning SAS^® by Example: A Programmer's Guide, Second Edition- By Ron Cody
2. Practical and Efficient SAS Programming: The Insider's Guide Book by Martha Messine
3. Data Management Solutions Using SAS® Hash Table Operations: A Business Intelligence Case Study-By Paul Dorfman and Don Henderson

That's immense!!!

[Dinurik]

Thank you!