How to differentiate between Select and SelectMany in LINQ?

When working with LINQ queries, it's important to understand the differences between the Select and SelectMany operations. Here's how you can differentiate between the two:

Select:

The Select method is used to transform elements in a collection by applying a specified transformation function to each element. It returns a new collection with the transformed elements.

Example:

var numbers = new List { 1, 2, 3, 4 };
var squaredNumbers = numbers.Select(num => num * num);

In this example, the Select method multiplies each number in the 'numbers' collection by itself, resulting in a new collection of squared numbers.

SelectMany:

The SelectMany method is used to flatten a sequence of sequences. It projects each element of a sequence to an IEnumerable and flattens the resulting sequences into one sequence.

Example:

var listOfLists = new List<List> { new List { 1, 2 }, new List { 3, 4 } };
var flattenedList = listOfLists.SelectMany(list => list);

In this example, the SelectMany method flattens the list of lists into a single list by combining all the individual lists into one.

It's important to choose between Select and SelectMany based on the structure of your data and the desired outcome of your query when working with LINQ.