Chapter 9 - Querying and Manipulating Data with LINQ

1. What are the two required parts of LINQ?

   • A LINQ provider and the LINQ extension methods. You must import the System.Linq namespace to make the LINQ extension methods available and reference a LINQ provider assembly for the type of data that you want to work with.

2. Which LINQ extension method would you use to return a subset of properties from a type?

   • The Select method allows projection (selection) of properties.

3. Which LINQ extension method would you use to filter a sequence?

   • The Where method allows filtering by supplying a delegate (or lambda expression) that returns a Boolean to indicate whether the value should be included in the results.

   • List five LINQ extension methods that perform aggregation.

   • Max, Min, Count, Average, Sum, and Aggregate.

4. What is the difference between the Select and SelectMany extension methods?

   • Select returns exactly what you specify to return. SelectMany checks that the items you have selected are themselves IEnumerable<T> and then breaks them down into smaller parts. For example, if the type you select is a string value (which is IEnumerable<char>), SelectMany will break each string value returned into their individual char values.