Sort Dictionary by keys in C#

This post will discuss how to sort a dictionary by its keys in C#.

1. Using `SortedDictionary<TKey,TValue>`

You can’t sort a Dictionary<TKey,TValue> since it is implemented as a hash table. You can use SortedDictionary<TKey,TValue> instead, which represents a dictionary where key/value pairs are sorted on the key, and it is implemented as a binary search tree with logarithmic time retrieval operation.

The idea is to pass the regular dictionary to the SortedDictionary constructor, which will then initializes a new instance of the dictionary, containing the same mappings as the specified dictionary, but ordered according to the keys.

using System;

using System.Collections.Generic;

public static class Extensions

{

public static SortedDictionary<TKey, TValue> SortByKey<TKey, TValue>(

this IDictionary<TKey, TValue> dict)

{

return new SortedDictionary<TKey, TValue>(dict);

}

public class Example

{

public static void Main()

{

Dictionary<string, int> dict = new Dictionary<string, int>() {

{"A", 1}, {"B", 2}, {"C", 3}

};

var sortedDict = dict.SortByKey();

Console.WriteLine(String.Join(", ", sortedDict)); // [A, 1], [B, 2], [C, 3]

}

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2. Using Sorting

Alternatively, you can get a collection of keys present in the dictionary and sort it. Then, you can process each key-value pair for every key in the sorted collection. Note that this requires LINQ and you need to add System.Linq namespace.

using System;

using System.Linq;

using System.Collections.Generic;

public static class Extensions

{

public static void processInSortedOrder<TKey, TValue>(this IDictionary<TKey, TValue> dict)

{

foreach (var key in dict.Keys.OrderBy(x => x)) {

Console.WriteLine("{0}: {1}", key, dict[key]);

}