SelectRandom
This method selects a random element from an Enumerable with only one pass (O(N) complexity). It contains optimizations for argumens that implement ICollection<T> by using the Count property and the ElementAt LINQ method. The ElementAt LINQ method itself contains optimizations for IList<T>
Source
using System;
using System.Collections.Generic;
using System.Linq;
namespace Extensions
{
public static class EnumerableExtensions
{
private static Random random = new Random();
public static T SelectRandom<T>(this IEnumerable<T> sequence)
{
if(sequence == null)
{
throw new ArgumentNullException();
}
if (!sequence.Any())
{
throw new ArgumentException("The sequence is empty.");
}
//optimization for ICollection<T>
if (sequence is ICollection<T>)
{
ICollection<T> col = (ICollection<T>)sequence;
return col.ElementAt(random.Next(col.Count));
}
int count = 1;
T selected = default(T);
foreach (T element in sequence)
{
if (random.Next(count++) == 0)
{
//Select the current element with 1/count probability
selected = element;
}
}
return selected;
}
}
}
Example
int[] ints = new[] { 1, 2, 3, 4, 5 };
Console.WriteLine(ints.SelectRandom());
IEnumerable<int> seq = Enumerable.Range(1, 5);
Console.WriteLine(seq.SelectRandom());
Author: Stilgar
Submitted on: 16 okt. 2010
Language: C#
Type: System.Collections.Generic.IEnumerable<T>
Views: 8839