How do you sort a dictionary by value?

Question

I often have to sort a dictionary (consisting of keys & values) by value. For example, I have a hash of words and respective frequencies that I want to order by frequency.

There is a SortedList which is good for a single value (say frequency), that I want to map back to the word.

SortedDictionary orders by key, not value. Some resort to a custom class, but is there a cleaner way?

Answer 1

Use LINQ:

Dictionary<string, int> myDict = new Dictionary<string, int>(); myDict.Add("one", 1); myDict.Add("four", 4); myDict.Add("two", 2); myDict.Add("three", 3);  var sortedDict = from entry in myDict orderby entry.Value ascending select entry; 

This would also allow for great flexibility in that you can select the top 10, 20 10%, etc. Or if you are using your word frequency index for type-ahead, you could also include StartsWith clause as well.

Answer 2

Use:

using System.Linq.Enumerable; ... List<KeyValuePair<string, string>> myList = aDictionary.ToList();  myList.Sort(     delegate(KeyValuePair<string, string> pair1,     KeyValuePair<string, string> pair2)     {         return pair1.Value.CompareTo(pair2.Value);     } ); 

Since you're targeting .NET 2.0 or above, you can simplify this into lambda syntax -- it's equivalent, but shorter. If you're targeting .NET 2.0 you can only use this syntax if you're using the compiler from Visual Studio 2008 (or above).

var myList = aDictionary.ToList();  myList.Sort((pair1,pair2) => pair1.Value.CompareTo(pair2.Value));