Array Shuffle
This page was last reviewed on Apr 27, 2023.
Dot Net Perls
Shuffle. Shuffling an array randomly reorders all elements, with results that are mathematically correct. Some solutions exist but do not give high-quality random results.
Shuffle logic. Imagine an array—we generate an array of completely random numbers of the same size. Then we sort the original array based on the values in the random number array.
Array Shuffle Fisher-Yates
Example code. Here we see an approach to shuffling a string array that is not an optimized shuffle. But it 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.
Info The method here uses the KeyValuePair 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.
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", "dog", "bird", "ant" }; string[] shuffle = RandomizeStrings(arr); foreach (string s in shuffle) { Console.WriteLine(s); } } }
ant cat dog bird
The code stores a Random number generator as a static field. You can call the RandomizeStrings method repeatedly and will get good results.
A summary. We used a mathematically sound approach for shuffling an array. This method is not optimally fast. If you need performance, use an implementation of Fisher-Yates.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
This page was last updated on Apr 27, 2023 (edit).
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