How to access random item in list

Question

I have an ArrayList  and I need to be able to click a button and then randomly pick out a string from that list and display it in a messagebox   How would I go about doing this

User · Answer

I needed to more item instead of just one. So, I wrote this:

public static TList GetSelectedRandom<TList>(this TList list, int count)
       where TList : IList, new()
{
    var r = new Random();
    var rList = new TList();
    while (count > 0 && list.Count > 0)
    {
        var n = r.Next(0, list.Count);
        var e = list[n];
        rList.Add(e);
        list.RemoveAt(n);
        count--;
    }

    return rList;
}

With this, you can get elements how many you want as randomly like this:

var _allItems = new List<TModel>()
{
    // ...
    // ...
    // ...
}

var randomItemList = _allItems.GetSelectedRandom(10);

User · Answer

ArrayList ar   new ArrayList            ar Add 1           ar Add 5           ar Add 25           ar Add 37           ar Add 6           ar Add 11           ar Add 35           Random r   new Random            int index   r Next 0 ar Count-1           MessageBox Show ar index  ToString

User · Answer

Create a Random instance   Random rnd   new Random      Fetch a random string   string s   arraylist rnd Next arraylist Count      Remember though  that if you do this frequently you should re-use the Random object  Put it as a static field in the class so it s initialized only once and then access it

User · Answer

I usually use this little collection of extension methods   public static class EnumerableExtension       public static T PickRandom lt T gt  this IEnumerable lt T gt  source                return source PickRandom 1  Single               public static IEnumerable lt T gt  PickRandom lt T gt  this IEnumerable lt T gt  source  int count                return source Shuffle   Take count              public static IEnumerable lt T gt  Shuffle lt T gt  this IEnumerable lt T gt  source                return source OrderBy x   gt  Guid NewGuid               For a strongly typed list  this would allow you to write   var strings   new List lt string gt     var randomString   strings PickRandom      If all you have is an ArrayList  you can cast it   var strings   myArrayList Cast lt string gt

User · Answer

Why not 2    public static T GetRandom lt T gt  this List lt T gt  list         return list  int  DateTime Now Ticks list Count

User · Answer

Create an instance of Random class somewhere  Note that it s pretty important not to create a new instance each time you need a random number  You should reuse the old instance to achieve uniformity in the generated numbers  You can have a static field somewhere  be careful about thread safety issues    static Random rnd   new Random     Ask the Random instance to give you a random number with the maximum of the number of items in the ArrayList   int r   rnd Next list Count    Display the string   MessageBox Show  string list r

User · Answer

Why not   public static T GetRandom lt T gt  this IEnumerable lt T gt  list       return list ElementAt new Random DateTime Now Millisecond  Next list Count

User · Answer

You can do   list OrderBy x   gt  Guid NewGuid    FirstOrDefault

User · Answer

Printing randomly country name from JSON file     Model   public class Country               public string Name   get  set            public string Code   get  set            Implementaton    string filePath   Path GetFullPath Path Combine Environment CurrentDirectory                     Data Country json               string  countryJson   File ReadAllText filePath               var  country   JsonConvert DeserializeObject lt List lt Country gt  gt   countryJson                 int index   random Next  country Count               Console WriteLine  country index  Name

User · Answer

I ll suggest different approach  If the order of the items inside the list is not important at extraction  and each item should be selected only once   then instead of a List you can use a ConcurrentBag which is a thread-safe  unordered collection of objects   var bag   new ConcurrentBag lt string gt     bag Add  Foo    bag Add  Boo    bag Add  Zoo      The EventHandler   string result  if  bag TryTake out result         MessageBox Show result       The TryTake will attempt to extract an  random  object from the unordered collection

User · Answer

Or simple extension class like this   public static class CollectionExtension       private static Random rng   new Random         public static T RandomElement lt T gt  this IList lt T gt  list                return list rng Next list Count               public static T RandomElement lt T gt  this T   array                return array rng Next array Length              Then just call   myList RandomElement      Works for arrays as well   I would avoid calling OrderBy   as it can be expensive for larger collections  Use indexed collections like List lt T gt  or arrays for this purpose

User · Answer

I have been using this ExtensionMethod for a while   public static IEnumerable lt T gt  GetRandom lt T gt  this IEnumerable lt T gt  list  int count        if  count  lt   0        yield break      var r   new Random        int limit    count   10       foreach  var item in list OrderBy x   gt  r Next 0  limit   Take count         yield return item

[c#] How to access random item in list?

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