How to code this column (point)?

[heretolearnSAS]

cust_no	date	obs_window	point
abc123	201801	1	0
abc123	201802	1	1
abc123	201803	1	2
abc123	201804	1	3
abc123	201805	2	0
abc123	201806	2	1
abc123	201807	2	2
def456	201803	1	0
def456	201804	1	1
def456	201805	2	0
def456	201806	2	1
def456	201807	2	2

Hello guys, let's assume the above is my dataset, and the "point" is the column I want to create. In this case, I wish to create the input for the "point" column starting with 0 for the first observed observation of each customer, and +1 thereafter. However, if obs_window is different, then the point will restart again for a customer.

the current code I'm using is as below:

data mydataset;

set dataset;

by cust_no;

if first.cust_no then point = 0;

else point +1;

in this case, how should I tune the above code?

[japelin · Accepted solution]

I assume it is sorted by cust_no obs_window.

data mydataset;
set have;
by cust_no obs_window;
if first.obs_window then point = 0;
else point +1;
run;