How Can I Flatten a Nested IEnumerable in LINQ?

Using LINQ to flatten nested IEnumerable

In LINQ, you may encounter nested IEnumerables that need to be "flattened" to obtain a single merged IEnumerable. This flattening process becomes necessary when the inner IEnumerable contains elements of the same type as the outer IEnumerable.

Case Study:

Consider the examples provided:

<code>IEnumerable<List<int>> iList = from number in
    (from no in Method() select no) select number;</code>

In this example, iList represents a nested IEnumerable, where each element is itself a List. The goal is to merge all these nested lists into a single List.

Solution: SelectMany()

LINQ provides the SelectMany() method, which is specifically used to flatten nested IEnumerable collections. It iterates over the outer IEnumerable and projects each inner collection element into a new IEnumerable.

To get the desired result you can use SelectMany() as follows:

<code>var result = iList.SelectMany(i => i);</code>

In this code, the SelectMany() method takes each list contained in iList (represented by the variable i) and concatenates the elements of that list into a new flattened IEnumerable named result.

Example:

With this flattening, the original nested arrays [1,2,3,4] and [5,6,7] will be combined into a single array [1,2,3,4,5,6,7] as expected ].

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