Dictionary Extension LINQ List SortedSet ToList

`Remove` duplicates, `List`

A VB.NET List may contain unneeded duplicate elements. We remove duplicates in many ways, with loops, with algorithms of varying speed.

But with the Distinct extension method, we remove these duplicates with a single function call. Collections like the SortedSet can be used to dedupe as we go along.

An example

The Distinct method is part of System.Linq. We need a newer version of VB.NET to use it. Distinct internally loops over all elements in the collection and eliminates duplicates.

Start We create a list with some duplicate numbers. After we call Distinct and convert it back into a List, we have a list of 1, 2 and 3.

Then We need to invoke ToList, another extension, after calling Distinct to convert back into a list.

Note Distinct returns an IEnumerable collection, not a List. But with ToList we convert it easily back into a List.

Module Module1
    Sub Main()
        ' Create list and add values.
        Dim values As List(Of Integer) = New List(Of Integer)
        values.Add(1)
        values.Add(2)
        values.Add(2)
        values.Add(3)
        values.Add(3)
        values.Add(3)

        ' Filter distinct elements, and convert back into list.
        Dim result As List(Of Integer) = values.Distinct().ToList

        ' Display result.
        For Each element As Integer In result
            Console.WriteLine(element)
        Next
    End Sub
End Module1
2
3

`Dictionary`, `SortedSet`

Consider adding elements to a Dictionary or a SortedSet to eliminate duplicates as we go along. You can use Keys and ToList to get a List from a Dictionary.

Often problems can be solved in simple, or complex, ways. For removing duplicates from a list, loops may be used. But this may lead to greater total program complexity.

Remove duplicates, List

An example

Dictionary, SortedSet

`Remove` duplicates, `List`

`Dictionary`, `SortedSet`