create serial number

[Ronein]

Hello

I want to create a new column called "Key".

For each customer there will be unique value from row with ind=1 until one row before the next ind=1.

What is the way to do it please?

Data have;
Input CustomerID Ind amount;
cards;
111 1 5000
111 0 200
111 0 210
111 0 205
111 0 208
111 1 8000
111 0 71
111 0 72
111 0 75
111 1 20000
222 1 7000
222 0 400
222 0 412
222 1 10000
222 0 101
222 0 99
222 0 102
;
Run;

Wanted data set

[PeterClemmensen]

Data have;
Input CustomerID Ind amount;
cards;
111 1 5000  
111 0 200   
111 0 210   
111 0 205   
111 0 208   
111 1 8000  
111 0 71    
111 0 72    
111 0 75    
111 1 20000 
222 1 7000  
222 0 400   
222 0 412   
222 1 10000 
222 0 101   
222 0 99    
222 0 102   
;

data want;
   set have;
   by CustomerID;
   if Ind = 1 or first.CustomerID then key + 1;
run;