Flatten a C# Dictionary of Lists with Linq

Question

I have a Dictionary in C#:

Dictionary<string, List<string>> 

How can I use Linq to flatten this into one List<string> that contains all of the lists in the Dictionary?

Thanks!

Answer 1

Very easily:

var list = dictionary.Values              // To get just the List<string>s                      .SelectMany(x => x)  // Flatten                      .ToList();           // Listify 

Here the SelectMany call takes a sequence of inputs (the lists which make the values of the dictionary) and projects each single input into another sequence of outputs - in this case "the elements of the list". It then flattens that sequence of sequences into a single sequence.

Answer 2

as a query

var flattened = from p in dictionary                 from s in p.Value                 select s; 

or as methods...

var flattened = dictionary.SelectMany(p => p.Value); 

I like this over what others have done as I'm passing the whole dictionary into the Linq query rather than just the values.