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Retrieve N number of random items from a Generic List

This is a snippet that first randomizes a Generic List, then retrieve N number of items

Submitted By: PsychoCoder

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Rating:

Views: 528

Language: C#

Last Modified: July 5, 2009

Instructions: Add the following to your class
using System.Collections;
using System.Collections.Generic;
using System.Linq

Requires .Net 3.5 or higher

Snippet

/// <summary>
/// method for returning N number of random items from a generic list
/// </summary>
/// <typeparam name="T">Item type</typeparam>
/// <param name="list">Generic list we wish to retrieve from</param>
/// <param name="count">number of items to return</param>
/// <returns></returns>
public IEnumerable<T> RandomizeGenericList<T>(List<T> list, int count)
{
List<T> randomList = new List<T>();
Random random = new Random();
while (list.Count > 0)
{
//get the next random number between 0 and
//the list count
int idx = random.Next(0, list.Count);
//get that index
randomList.Add(list[idx]);
//remove that item so it cant
//be added again
list.RemoveAt(idx);
}
//return the specified number of items
return randomList.Take(count);
}
Sample usage:
public IEnumerable<SomeItem> GetRandomItems(int count)
{
List<SomeItem> list = new List<SomeItem>();
//...add your items here
return RandomizeGenericList(list, count);
}

Copy & Paste

/// <summary>
/// method for returning N number of random items from a generic list
/// </summary>
/// <typeparam name="T">Item type</typeparam>
/// <param name="list">Generic list we wish to retrieve from</param>
/// <param name="count">number of items to return</param>
/// <returns></returns>
public IEnumerable<T> RandomizeGenericList<T>(List<T> list, int count)
{
    List<T> randomList = new List<T>();
    Random random = new Random();

while (list.Count > 0)
    {
        //get the next random number between 0 and
        //the list count
        int idx = random.Next(0, list.Count);

//get that index
        randomList.Add(list[idx]);

//remove that item so it cant
        //be added again
        list.RemoveAt(idx);
    }

//return the specified number of items
    return randomList.Take(count);
}

Sample usage:
public IEnumerable<SomeItem> GetRandomItems(int count)
{
    List<SomeItem> list = new List<SomeItem>();

//...add your items here

return RandomizeGenericList(list, count);
}

Comments
Martyr2 2009-07-05 16:44:55
Be advised that the method "Take" was introduced in .NET 3.5 and you are also required to have the System.Linq namespace in there to get access to the method for the List generic type.
PsychoCoder 2009-07-05 17:55:27
Thanks Martyr2, I forgot all about that. I'll add that now