Flatten sequences with the C# LINQ SelectMany operator

Suppose that we have an object with a collection of other objects, like a customer with order items. Then we can also have a sequence of customers where each customer will have her own list of orders. It happens that we want to analyse all orders regardless of the customer, like how many of product A have been sold. There are several options to collect all orders from all customers and place them into one unified collection for further analysis.

The C# SelectMany operator has been specifically designed to extract collections of objects and flatten those collections into one. This post will provide a couple of examples to demonstrate its usage.

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