Sort List

A VB.NET List can be sorted. The List type has a useful subroutine called Sort that will sort your List either by a default sorting order or with a custom one.

Type notes

Instead of using String instances in your List, you can use other types such as Integer or even Class types. All of these things can be sorted, but a lambda argument may be needed.

Sort with lambda

Here, we create a List of strings, and then call Sort with a lambda expression argument. Our lambda expression begins with the Function keyword and receives 2 String parameters.

Module Module1
    Sub Main()
        Dim l As List(Of String) = New List(Of String)
        l.Add("mississippi")
        l.Add("indus")
        l.Add("danube")
        l.Add("nile")

        ' Sort using lambda expression.
        l.Sort(Function(elementA As String, elementB As String)
                   Return elementA.Length.CompareTo(elementB.Length)
               End Function)

        For Each element As String In l
            Console.WriteLine(element)
        Next
    End Sub
End Module
nile
indus
danube
mississippi

Simple example

This example creates a List of three String instances. Then it invokes the Sort subroutine. This subroutine does not return a value—instead it changes the List to be sorted.

Module Module1
    Sub Main()
        Dim l As List(Of String) = New List(Of String)
        l.Add("tuna")
        l.Add("velvetfish")
        l.Add("angler")

        ' Sort alphabetically.
        l.Sort()

        For Each element As String In l
            Console.WriteLine(element)
        Next
    End Sub
End Module
angler
tuna
velvetfish

Reverse List

The Reverse subroutine inverts the order of the elements in the List from their original order. It does no sorting. As with Sort, you do not need to assign anything to the result.

Module Module1
    Sub Main()
        Dim l As List(Of String) = New List(Of String)
        l.Add("anchovy")
        l.Add("barracuda")
        l.Add("bass")
        l.Add("viperfish")

        ' Reverse list.
        l.Reverse()

        For Each element As String In l
            Console.WriteLine(element)
        Next
    End Sub
End Module
viperfish
bass
barracuda
anchovy

A summary

We can sort the elements in a List using the parameterless Sort subroutine and also with a lambda expression. It is possible to Reverse the order of the elements in your List.