Find duplicates in a string array in VB.Net-CodePudding

I'm trying to find duplicates in an array and put only the duplicates in an array. The code im using is the following

    Dim duplicates As List(Of String) =
               WithDuplicates.GroupBy(Function(n) n) _
               .Where(Function(g) g.Count() > 1) _
               .Select(Function(g) g.First) _
               .ToList()
    Dim DuplicatesOnly As String() = duplicates.ToArray

WithDuplicates is the Array that contains the duplicates. Before, I used a richtextbox instead of a array but I had to switch to an array because of threading. I don't know why my code isnt working anymore. Any ideas how I could get this working?

Edit: The code above does indeed work, another part of my code caused the error.

CodePudding user response：

This might help you:

Dim duplicates As List(Of String) = WithDuplicates.Distinct.Where(Function(el) Array.IndexOf(WithDuplicates, el) <> Array.LastIndexOf(WithDuplicates, el)).ToList

CodePudding user response：

You almost had it. You just need to select the key instead of the first.

Dim withDuplicates As New List(Of String) From {"a", "b", "c", "a", "c"}

Dim duplicates As List(Of String) =
    withDuplicates.GroupBy(Function(n) n).
    Where(Function(g) g.Count() > 1).
    Select(Function(g) g.Key).ToList()
Dim DuplicatesOnly As String() = duplicates.ToArray

Console.WriteLine(String.Join(", ", DuplicatesOnly))

a, c

CodePudding user response：

Your code works if there are duplicates. Jimi's first comment may be pertinent, but your question lacks that detail.

    Dim WithDuplicates As New List(Of String) From {"aa", "b", "c", "aa", "c", "AA", "c"}
    ' Dim WithDuplicates As New List(Of String) From {"aa", "b", "c"} ', "aa", "c", "AA", "c"}

    Dim duplicates() As String
    duplicates = WithDuplicates.GroupBy(Function(n) n).
                    Where(Function(g) g.Count() > 1).
                    Select(Function(g) g.First).ToArray