Question

Let’s say I have a fairly large IList<foo> where foo looks like this:

public class foo
{
    public string Region { get; set; }
    public string Territory { get; set; }
    public string Location { get; set; }
    public string Person { get; set; }
}

…is there a way, using a reasonably quick/ efficient expression, to “group” these foo items by Region, so I might end up with an IDictionary<string, IList<foo>> and have the string key be the Region property, with each subordinate IList<foo> containing only the foo records that match that region? (it would not have to be an IDictionary, that’s just to illustrate the gist of what I’m trying to do.) I want to present an interactive list to my MVC view organized this sort of way, without having to write something relatively complex or use a third-party library.

Answer 1

Yes – you want a Lookup:

var lookup = list.ToLookup(x => x.Region);

You can create a dictionary by grouping, but personally I prefer to use a lookup as it’s specifically designed for the “single key, multiple values” scenario.