Array of Integers Comparing Integers VB.NET - vb.net

Question

Basically I have and array of integers that vary in size. I need to compare each number to each other number and display which number is repeated. For example:
Dim ints() As Integer = {1,2,2,5,4,6}
The number that shows up more than once is 2.
How can I run through the array and compare each integer with the numbers in the array. I tried a for loop but it didn't return the value I was looking for. I am new to VB.NET and do not understand fully.

Answer 1

Dim ints() As Integer = {1,2,2,5,4,6}
Dim repeatedNumbers = ints.GroupBy(Function(intValue) intValue) _
.Where(Function(grp) grp.Count > 1)
For each grp in repeatedNumbers
Console.WriteLine("Number {0} is repeated {1} times", grp(0), grp.Count)
Next
What this code does:
We first call GroupBy, which groups items by their value. The Function gets the grouping key, in this case we simply group by the array's value itself. This call returns a sequence of
groups. There is one group for every unique value in the array. The
group contains all items that correspond to a unique value. So if a value appears twice in the array, there will be a group which contains two ints with this value.
We call Where to filter groups. We only want groups for which the count is greater than one, so that only duplicate values are considered.
We then loop through the result. grp(0) gives us the first number in the group (we could have picked any number in the group, since all numbers in a group are the same!) and the Count property gives us the number of repetitions.

Answer 2

I would try it with something like this:
Dim ints() As Integer = {1, 2, 2, 5, 4, 6}
Array.Sort(ints)
For i = 1 To ints.GetUpperBound(0)
If ints(i) = ints(i - 1) Then MessageBox.Show(String.Format("{0} is repeated", ints(i)))
Next
Doing it like this on a sorted array keeps down the nesting.
I've not tested this but it should be along the right lines.

Answer 3

You could use LINQ to find the duplicates:
Dim repeating = (From n In ints
Group By n Into Dups = Group
Where Dups.Count > 1
Select Dups.First).ToArray()
This returns an Array of integers which only contains numbers that are not unique in the original array.
So this displays the repeating number(s):
MessageBox.Show(String.Format("Duplicates found: {0}", String.Join(","c, repeating)))