Question

I don’t want check if an item with a value exists in the arraylist,

I want to know the best code for performance to get how many occurrences of the same item with the same value exists in an arraylist.

I can do something like

For Each s As string In myArrayList
[...]
Next

however is there a better code of that?

Answer 1

It sounds like you want to see how many times a particular element is repeated in a ArrayList. If so try the following

Dim table As New Dictionary(Of String, Integer)
For Each s As String in myArrayList
  Dim count As Integer = 0
  If table.TryGetValue(s, count) Then
    table(s) = count + 1
  Else 
    table(s) = 1
  End If
Next

For Each pair in table 
  If pair.Value >= 2 Then
    Console.WriteLine(pair.Key)
  End If
Next

Note: This assumes that you are using Visual Studio 2005 or higher. If not please let me know and I’ll provide a 2003 compatible answer