C# Shuffle Array: KeyValuePair and List

Use Random, List and KeyValuePair structs to effectively shuffle an array.

Shuffle. We can shuffle an array, randomly reordering all elements, with results that are mathematically correct. Some solutions exist but do not give high-quality random results.

Example. Here we see an approach to shuffling a string array that is not the classic, optimized Fisher-Yates shuffle. But this approach is mathematically random. It will not cause strange biases in your code.

And: This is true because it performs all the operations together, rather than one after another.

Fisher-Yates Shuffle

Info: The method here uses the KeyValuePair<T, V> data structure that is included in System.Collections.Generic.

Then: It allocates another array containing the string[] elements and pairs them with a random number. Finally, it sorts.


Important: We randomize the entire array all at once, which will result in consistently random results.

C# program that uses random shuffle algorithm using System; using System.Collections.Generic; using System.Linq; class Program { static Random _random = new Random(); static string[] RandomizeStrings(string[] arr) { List<KeyValuePair<int, string>> list = new List<KeyValuePair<int, string>>(); // Add all strings from array. // ... Add new random int each time. foreach (string s in arr) { list.Add(new KeyValuePair<int, string>(_random.Next(), s)); } // Sort the list by the random number. var sorted = from item in list orderby item.Key select item; // Allocate new string array. string[] result = new string[arr.Length]; // Copy values to array. int index = 0; foreach (KeyValuePair<int, string> pair in sorted) { result[index] = pair.Value; index++; } // Return copied array. return result; } static void Main() { string[] arr = new string[] { "cat", "animal", "abacus", "framework" }; string[] shuffle = RandomizeStrings(arr); foreach (string s in shuffle) { Console.WriteLine(s); } } } Output abacus framework cat animal

Random numbers. The code stores a Random number generator as a static field, which means you can call the RandomizeStrings method repeatedly and will get good results. More information on Random is available.Random

Discussion. This article previously showed a naive method that used OrderBy in LINQ, but was not mathematically sound. The current method is mathematically sound, as noted in Wikipedia. See "Comparison with other shuffling algorithms."orderby

Info: Wikipedia notes that this approach is sometimes faster in high-level languages. It is unlikely to be faster in the C# language.

Fisher-Yates shuffle: Wikipedia

Summary. We used a mathematically sound approach for shuffling an array. This method is not optimally fast, but for my use this wasn't important. If you need performance, use an implementation of Fisher-Yates.
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