How to detect an event on SAS and how to remove the observations that follow that event

[noemi_b]

Hi all,

I am using SAS University Edition v.9.4. and I am working on a dataset that detect when a customer is about to churn from a bank.

Now, I need the following task to be performed by SAS and hoefully you can help. But first, let me provide you with a small datastep of my sample:

data have;
input customer_id_ano year month churn;
cards;
1 2017 1 0
1 2017 2 0
1 2017 3 0
1 2017 4 0
1 2017 5 0
1 2017 6 0
1 2017 7 0
1 2017 8 0
1 2017 9 1
1 2017 10 1
1 2017 11 1
1 2017 12 1
2 2017 1 0
2 2017 2 0
2 2017 3 0
2 2017 4 1
2 2017 5 1
2 2017 6 1
2 2017 7 1
2 2017 8 1
2 2017 9 1
2 2017 10 1
2 2017 11 1
2 2017 12 1
3 2017 1 1
3 2017 2 1
3 2017 3 1
3 2017 4 1
3 2017 5 1
3 2017 6 1
3 2017 7 1
3 2017 8 1
3 2017 9 1
3 2017 10 1
3 2017 11 1
3 2017 12 1
4 2017 1 0
4 2017 2 0
4 2017 3 0
4 2017 4 1
4 2017 5 1
4 2017 6 1
4 2017 7 1
4 2017 8 1
4 2017 9 1
4 2017 10 1
4 2017 11 1
4 2017 12 1
5 2017 1 0
5 2017 2 1
5 2017 3 1
5 2017 4 1
5 2017 5 1
5 2017 6 1
5 2017 7 1
5 2017 8 1
5 2017 9 1
5 2017 10 1
5 2017 11 1
5 2017 12 1
;
run;

Now, what I need is SAS to detect when the variable churn is 1 for the first time and delete all the observations following that event. In other words, instead of a list of 1s following the first churn event, I only need to keep the first 1 and delete the remaining ones. 

Let´s take customer_id_ano 1 as an example. We can see from the data step above that the variable churn for this customer is 1 starting from September 2017 and it remains 1 until the end of the observation period. Well, I only want the first churn=1 that occurred in September to remain in my dataset and the following observation must be dropped from it. 

I hope I managed to explai myself. And I would like to thank you in advance for the help you always provide to all the SAS beginners like me. Very appreciated!!

[Kurt_Bremser · Accepted solution]

Would this solve your task?

data want;
set have;
by customer_id_ano churn notsorted;
if churn = 0 or first.churn;
run;

[noemi_b]

thank you @Kurt_Bremser! I will acknowledge you in my thesis 😄