How Can LINQ's SelectMany() Method Flatten a Nested List of Integers?

Using LINQ's SelectMany() to Flatten Nested Integer Lists

LINQ queries often produce nested collections, like IEnumerable<List<int>>. The SelectMany() method efficiently flattens these into a single list.

The Challenge:

Suppose a LINQ query returns a list of lists of integers (IEnumerable<List<int>>). The task is to combine these inner lists into a single, one-dimensional List<int>.

Illustrative Example:

Starting with these input lists:

<code>[1, 2, 3, 4] and [5, 6, 7]</code>

The desired output is:

<code>[1, 2, 3, 4, 5, 6, 7]</code>

Solution with SelectMany():

LINQ's SelectMany() simplifies this process. Here's how to flatten the nested list:

<code class="language-csharp">var nestedList = new List<List<int>> { new List<int> { 1, 2, 3, 4 }, new List<int> { 5, 6, 7 } };
var flattenedList = nestedList.SelectMany(innerList => innerList).ToList(); </code>

Explanation:

• nestedList: This represents the input list of lists.
• SelectMany(innerList => innerList): This is the core of the solution. SelectMany() iterates through each innerList in nestedList. The lambda expression innerList => innerList simply projects each inner list onto itself, effectively unwrapping the nesting.
• .ToList(): This converts the resulting flattened sequence into a List<int>.

This concise code efficiently flattens the nested list, providing the desired single-dimensional list of integers.

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