Question: I have an array of Customer[] objects, and I want to use it to create a Dictionary<Customer, string>. What is the easiest way to examine the array for duplicates before I load the Dictionary? I want to avoid "ArgumentException: An item with the same key has already been added". Thanks.

Answer: 
Just call Dictionary.ContainsKey(key) before you add your Customers.
How big is the array? and how likely is it that there will be duplicates?

Checking each element of the array against all the others is quite a expensive operation.

It would be quicker to call `Dictionary.ContainsKey(key)` before adding each item.

**NOTE:** If duplicates are rare then you could use exception handling, but that's bad programming practice.