Sort a dictionary by a custom order

Question

This refers to

Sort a list by a custom order

I will go for a similar example... I have a dictionary containing users

public class UserInfo
{
    public string Name { get; set; }

    public string Location { get; set; }
}

the data:

private Dictionary<string, UserInfo> users = new Dictionary<string, UserInfo>(); // id + user

and a list of possible locations

        private string[] locations = {
            "europe",
            "america",
            "asia",
            "africa"
        };

how can I order this dictionary by these locations?

There should be the output

// ... all europeans

// ... all americans

// ... all asians

// ... all africans

when calling

    Dictionary<string, UserInfo> sortedUsers = ; // Sorting the dict "users" by locations

    foreach (KeyValuePair<string, UserInfo> info in sortedUsers)
    {
        Console.WriteLine("L: " + info.Value.Location + " N: " + info.Value.Name);
    }

Answer 1

A dictionary isn't an ordered collection, but it seems you want it's Values to be ordered:

var orderedUsersByLocation = users.Values.OrderBy(ui => ui.Location);

If you want a List<UserInfo> use ToList:

List<UserInfo> result = orderedUsersByLocation.ToList();

---

Maybe i didn't get the meaning of the string[] of possible locations, do you mean this array specifies the order and those locations are the possible locations in the UserInfo.Location?

private string[] locations = {
        "europe",
        "america",
        "asia",
        "africa"
    };

var orderedUsersByLocation = users.Values
    .OrderBy(ui => Array.IndexOf(locations, ui.Location));

If it's possible that a location is not contained in that array Array.IndexOf returns -1, so those entries will be first. If that's possible and you want them to be listed last:

var orderedUsersByLocation = users.Values
    .Select(ui => new { UserInfo = ui, Index = Array.IndexOf(locations, ui.Location)})
    .OrderBy(x => x.Index == - 1 ? int.MaxValue : x.Index)
    .Select(x => x.UserInfo);

Answer 2

Dictionary isn't an ICollection, you'll cannot use OrderBy(), but if you convert to list, you can instanciate an IComparer function :

private class SortCustom : IComparer
{
   private static string[] locations = {
        "europe",
        "america",
        "asia",
        "africa"
    };
   int IComparer.Compare(UserInfo a, UserInfo b)
   {
      return 
           Array.FindIndex(locations, row => row == a.Value.Location).CompareTo(
           Array.FindIndex(locations, row => row == b.Value.Location));
   }
}

Called by :

sortedUsers.OrderBy(x => x, new SortCustom());

Answer 3

You don't sort a dictionary, you get its values as a list and sort the values based on your criteria, which incidentally would be easiest to do if the criteria were a dictionary:

Dictionary<string,int> locations = new Dictionary<string,int>();
locations["europe"] = 0;
locations["america"] = 1;
locations["asia"] = 2;
locations["africa"] = 3;

//formatted to fit in SO without scrolling
var sortedUsers = 
  users.Values.OrderBy(
    u => locations.ContainsKey(u.Location) ? locations[u.Location] : 999999
  );

foreach (UserInfo info in sortedUsers)
{
    Console.WriteLine("L: " + info.Value.Location + " N: " + info.Value.Name);
}

Answer 4

You can try to order by your "custom location order" like this:

string[] locations = 
{
    "europe",
    "america",
    "asia",
    "africa"
};

Dictionary<string, UserInfo> sortedUsers = new Dictionary<string, UserInfo>();

foreach (var item in locations)
{
    sortedUsers = sortedUsers.Concat(users.Where(u => u.Value.Location == item)
                             .ToDictionary(d => d.Key, d => d.Value))
                             .ToDictionary(d => d.Key, d => d.Value);
}

Answer 5

You could at first build a sorted list by using IComparer and then create a dictionary from it:

    void Main()
    {
        var d = GetDictionary();
    }

    Dictionary<string,UserInfo> GetDictionary()
    {
        var l = new List<UserInfo>() {
            new UserInfo("One", "There"),
            new UserInfo("Two", "SomewhereB"),
            new UserInfo("Three", "SomewhereA"),
            new UserInfo("Four", "Here")
        };
        var comp = new UserInfoComparer();
        l.Sort(comp);
        return  l.ToDictionary( e => e.Name);
    }

    public class UserInfo
    {
        public string Name { get; set; }
        public string Location { get; set; }
        public UserInfo(string name, string location)
        {
            Name = name;
            Location = location;
        }
    }
    public class UserInfoComparer: IComparer<UserInfo>{
        public int Compare(UserInfo x, UserInfo y)
        {
            var r = x.Location.CompareTo(y.Location);
            if (r == 0)
            {
                r = x.Name.CompareTo(y.Name);
            }
            return r;
        }
    }