How do you sort a dictionary by value? – Dev

The best answers to the question “How do you sort a dictionary by value?” in the category Dev.

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 it back to the word.

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

ANSWER:

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));

ANSWER:

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:

Looking around, and using some C# 3.0 features we can do this:

foreach (KeyValuePair<string,int> item in keywordCounts.OrderBy(key=> key.Value))
{ 
    // do something with item.Key and item.Value
}

This is the cleanest way I’ve seen and is similar to the Ruby way of handling hashes.

ANSWER:

var ordered = dict.OrderBy(x => x.Value).ToDictionary(x => x.Key, x => x.Value);