Imagine you are working for a company that have, let's say it has 10 branches. Your task is to create lists for A/B testing, so you need to prepare a new colum classifies customers in category A or B. (Group by Bank)
So you can have a table like this.
In an Ideal world you will have even number of customer, so for eks 80 can be divided in 40 A and 40 B, but in reallity odd figures will appear so for eks 81, then it will be 40 A and 41 B.