How to Return Elements When the Result Is a Sequence (Select Many)

The SelectMany standard query operator flattens out any IEnumerable<T> result elements, returning each element individually from those enumerable sources before moving onto the next element in the result sequence. In contrast, the Select extension method would stop at the first level and return the IEnumerable<T> element itself.

Listing 3-8 demonstrates how SelectMany differs from Select, with each variation aiming to retrieve each individual word within a set of phrase strings. To retrieve the words in Option 1, a sub for loop is required, but SelectMany automatically performs this subiteration of the original result collection, as shown in Option 2. Option 3 demonstrates that the same result can be achieved using multiple from statements in a query expression (which maps the query to use SelectMany operator behind the scenes). The Console output is shown in Output 3-5.