Question

Lets say I have a flat list of objects, each of which has a person’s name, and a single Role they’re in, like so:

        var People = new[] { 
            new PersonRole(){ Name = "Adam", Role = "R1" },
            new PersonRole(){ Name = "Adam", Role = "R2" },
            new PersonRole(){ Name = "Adam", Role = "R3" },
            new PersonRole(){ Name = "Bob", Role = "R1" },
        };

Now, is there a direct way to get this into a Dictionary<string, List<string>> based on Name and Role (obviously). I did it in two steps, like below, but I have to think there’s a more direct way.

Dictionary<string, List<string>> resultLookup = 
   People.Select(p => p.Name).Distinct().ToDictionary(str => str, str => new List<string>());

People.ForEach(p => resultLookup[p.Name].Add(p.Role));

Thanks!

Answer 1

var dict = People.ToLookup(p=>p.Name, p=>p.Role)
  .ToDictionary(it=>it.Key, it=>it.ToList());