C#: Remove duplicate values from dictionary?

Question

How can I create a dictionary with no duplicate values from a dictionary that may have duplicate values?

IDictionary<string, string> myDict = new Dictionary<string, string>();

myDict.Add("1", "blue");
myDict.Add("2", "blue");
myDict.Add("3", "red");
myDict.Add("4", "green");


uniqueValueDict = myDict.???

Edit:

-I don't care which key is kept. - Is there something using Distinct() operation?

Answer 1

What do you want to do with the duplicates? If you don't mind which key you lose, just build another dictionary like this:

IDictionary<string, string> myDict = new Dictionary<string, string>();

myDict.Add("1", "blue");
myDict.Add("2", "blue");
myDict.Add("3", "red");
myDict.Add("4", "green");

HashSet<string> knownValues = new HashSet<string>();
Dictionary<string, string> uniqueValues = new Dictionary<string, string>();

foreach (var pair in myDict)
{
    if (knownValues.Add(pair.Value))
    {
        uniqueValues.Add(pair.Key, pair.Value);
    }
}

That assumes you're using .NET 3.5, admittedly. Let me know if you need a .NET 2.0 solution.

Here's a LINQ-based solution which I find pleasantly compact...

var uniqueValues = myDict.GroupBy(pair => pair.Value)
                         .Select(group => group.First())
                         .ToDictionary(pair => pair.Key, pair => pair.Value);

Answer 2

The brute-force solution would be something like the following

var result = dictionary
    .GroupBy(kvp => kvp.Value)
    .ToDictionary(grp => grp.First().Value, grp.Key)

assuming you don't really care about the key used to represent a group of duplicates and it is acceptable to rebuild the dictionary.

Answer 3

Jon beat me to the .NET 3.5 solution, but this should work if you need a .NET 2.0 solution:

        List<string> vals = new List<string>();
        Dictionary<string, string> newDict = new Dictionary<string, string>();
        foreach (KeyValuePair<string, string> item in myDict)
        {
            if (!vals.Contains(item.Value))
            {
                newDict.Add(item.Key, item.Value);
                vals.Add(item.Value);
            }
        }

Answer 4

foreach (var key in mydict.Keys)
  tempdict[mydict[key]] = key;
foreach (var value in tempdict.Keys)
  uniquedict[tempdict[value]] = value;

Answer 5

Dictionary<string, string> test = new Dictionary<string,string>();
test.Add("1", "blue");
test.Add("2", "blue");
test.Add("3", "green");
test.Add("4", "red");
Dictionary<string, string> test2 = new Dictionary<string, string>();
foreach (KeyValuePair<string, string> entry in test)
{
    if (!test2.ContainsValue(entry.Value))
        test2.Add(entry.Key, entry.Value);
}

Answer 6

This is how I did it:

                dictionary.add(control, "string1");
                dictionary.add(control, "string1");
                dictionary.add(control, "string2");
              int x = 0;
        for (int i = 0; i < dictionary.Count; i++)
        {         
            if (dictionary.ElementAt(i).Value == valu)
            {
                x++;
            }
            if (x > 1)
            {
                dictionary.Remove(control);
            }
        }

Answer 7

Just a footnote to those using the Revit API, this is one method that works for me in removing duplicate elements, when you can't use say wallType as your object type and instead need to leverage raw elements. it's a beaut mate.

  //Add Pair.value to known values HashSet
                 HashSet<string> knownValues = new HashSet<string>();

                Dictionary<Wall, string> uniqueValues = new Dictionary<Wall, string>();

                 foreach (var pair in wall_Dict)
                 {
                     if (knownValues.Add(pair.Value))
                     {
                         uniqueValues.Add(pair.Key, pair.Value);
                     }
                 }

Answer 8

In addition to the answer of Jon Skeet , if your value is an intern object you can use :

var uniqueValues = myDict.GroupBy(pair => pair.Value.Property)
                     .Select(group => group.First())
                     .ToDictionary(pair => pair.Key, pair => pair.Value);

This way you will remove the duplicate only on one property of the object