c# linq GroupBy on the values of a List within a List

Question

I have a List of Objects and within the Object there is a List of strings. What I want to do is find out how many of each string value there are.

So to create a simple example with the languages spoken by people in a team.

public class PeopleLanguages
{
    public string Name;
    public List<string> Languages;
}

Create the test data...

List<PeopleLanguages> peopleLanguages = new List<PeopleLanguages>();

peopleLanguages.Add(new PeopleLanguages { Name = "Rod", Languages = new List<string> { "English", "French", "German" } });
peopleLanguages.Add(new PeopleLanguages { Name = "Jane", Languages = new List<string> { "English", "Spanish", "Greek" } });
peopleLanguages.Add(new PeopleLanguages { Name = "Fredie", Languages = new List<string> { "French", "Arabic", "Italian" } });
peopleLanguages.Add(new PeopleLanguages { Name = "Viktor", Languages = new List<string> { "English", "Krakozhian" } });

To visualise the data:

 * Rod => English | French | German
 * Jane => English | Spanish | Greek
 * Fredie => French | Arabic | Italian
 * Viktor => English | Krakozhian

I can get the result I want by finding the distinct string values using SelectMany().Distinct() then matching within a foreach loop:

foreach (string language in peopleLanguages.SelectMany(p => p.Languages).Distinct())
{
    Console.WriteLine($"{language} = {peopleLanguages.Where(p => p.Languages.Contains(language)).Count()}");
}

Output:

English = 3
French = 2
German = 1
Spanish = 1
Greek = 1
Arabic = 1
Italian = 1
Krakozhian = 1

But there has to be a better way to do this using GroupBy().

I'm just stuck about how to get the individual distinct values out of the List of languages.

Answer 1

Demo on dotnet fiddle

You can use SelectMany to get a list of list langues, then GroupBy as you wish like below

var result = peopleLanguages
    .SelectMany(p => p.Languages)
    .GroupBy(p => p);
    
foreach(var item in result)
{
    Console.WriteLine($"{item.Key} : {item.Count()}");
}

Output

English : 3
French : 2
German : 1
Spanish : 1
Greek : 1
Arabic : 1
Italian : 1
Krakozhian : 1