VB.NET - Sort Examples - Dot Net Perls

Sort. Elements, one after another, proceed in order. But often collections are not in an order we want. With the VB.NET Sort subroutine we order elements by their values.

Sorting details. We sort collections in-place. Sorting is by default in ascending order: elements go from lowest to highest. We can implement a descending order.

Array. First, we can use Array.Sort on array instances. Here the array is of type String() and it contains 3 strings (vegetables). Array.Sort is called.

And The array is sorted in-place. Then we loop through the array with a For-Each loop, and finally we print results.

For

Module Module1 Sub Main() ' Create an array of String() with 3 elements. Dim vegetables As String() = New String() {"turnip", "onion", "corn"} ' Use the System.Array.Sort shared method. System.Array.Sort(vegetables) ' Loop through the results and print them with Console.WriteLine. For Each value As String In vegetables Console.WriteLine(value) Next End Sub End Module

corn onion turnip

Sort, Reverse. Another way to reorder an array combines the Sort and Reverse methods. Effectively, this will give you a reverse alphabetical sort on strings.

Tip It is important to use Reverse after Sort, because Sort will always produce an alphabetical array in this context.

Module Module1 Sub Main() ' Create a String array with 5 elements. Dim array As String() = New String() {"X", _ "B", _ "A", _ "Z", _ "C"} ' Use the System.Array.Sort shared method. System.Array.Sort(Of String)(array) ' Invoke the Reverse method after sorting. System.Array.Reverse(array) ' Loop through the results. For Each value As String In array Console.WriteLine(value) Next End Sub End Module

Z X C B A

Sort, descending. Here is a better way to sort descending (from last to first) in VB.NET. No separate reverse call is needed. Instead, we use a special Comparison Function.

Info In DescendingComparison, we create a descending sort by changing the order of the variables in the CompareTo call.

CompareTo

Tip We use AddressOf to reference our special Comparison Function. Then we use For-Each to display the result.

Module Module1 Function DescendingComparison(ByVal valueA As String, ByVal valueB As String) As Integer ' Invert the order of the comparison to sort in descending order. Return valueB.CompareTo(valueA) End Function Sub Main() Dim letters As String() = {"X", "B", "A", "Z", "C"} ' Use custom DescendingComparison to sort in reverse. Array.Sort(Of String)(letters, New Comparison(Of String)(AddressOf DescendingComparison)) ' Display results. For Each value As String In letters Console.WriteLine("DESCENDING: {0}", value) Next End Sub End Module

DESCENDING: Z DESCENDING: X DESCENDING: C DESCENDING: B DESCENDING: A

List. Sorting a List is also easy. No custom algorithms need to be implemented. Instead, you can invoke the instance Sort method on the List you created.

Sort List

Info Internally, this uses similar code to the System.Array.Sort method so performance is similar.

Next In this program, we sort the room objects (furniture) and then print them out to the screen.

Module Module1 Sub Main() ' Create a List of Strings and add 4 Strings to it. Dim list As New List(Of String) list.Add("chair") list.Add("table") list.Add("desk") list.Add("couch") ' Use Sort method. list.Sort() ' Loop through the results and display them. For Each value As String In list Console.WriteLine(value) Next End Sub End Module

chair couch desk table

List, sort with lambda. With a List, we can use a lambda expression to define the Comparison Function. This may make the VB.NET code shorter and easier to read.

Here We create a List of 3 integers, and then Sort it in descending (high to low) order, using a lambda expression.

List

Lambda

Module Module1 Sub Main() Dim numbers = New List(Of Integer)({20, 30, 40}) ' Use lambda to sort list in descending order. numbers.Sort(Function(valueA, valueB) valueB.CompareTo(valueA)) For Each number As Integer In numbers Console.WriteLine("LAMBDA SORTED NUMBER: {0}", number) Next End Sub End Module

LAMBDA SORTED NUMBER: 40 LAMBDA SORTED NUMBER: 30 LAMBDA SORTED NUMBER: 20

Copied array, sort. Array.Sort() operates on the original data. So we must make a copy of the original array if we wish to keep it in that order. We apply the Array.Copy Function.

Array.Copy

Note The changes you make to one copy of the array are not reflected in the other. The 2 arrays are in separate, unconnected memory.

Module Module1 Sub Main() Dim names() As String = {"Zach", "Andrew", "David"} ' Create a copy of names array and sort it. Dim namesCopy(2) As String Array.Copy(names, namesCopy, 3) Array.Sort(namesCopy) ' Display arrays. Console.WriteLine(String.Join(",", names)) Console.WriteLine(String.Join(",", namesCopy)) End Sub End Module

Zach,Andrew,David Andrew,David,Zach

Sort on 2 items. Support we have a List of Tuples, and we want to sort based on the first value of each tuple, and then the second value. Here we use an ascending and also descending sort.

Info ComparisonTwoTuples receives 2 tuples and returns an Integer. We call CompareTo—if the first comparison is 0, we use a second comparison.

Result The list is sorted ascending on the first Integer in each tuple, and then descending on the second Integer.

Module Module1 Function GetData() As List(Of Tuple(Of Integer, Integer)) Dim result As New List(Of Tuple(Of Integer, Integer)) result.Add(New Tuple(Of Integer, Integer)(100, 1)) result.Add(New Tuple(Of Integer, Integer)(100, 2)) result.Add(New Tuple(Of Integer, Integer)(10, 2)) result.Add(New Tuple(Of Integer, Integer)(10, 1)) Return result End Function Function ComparisonTwoTuples(ByVal tupleA As Tuple(Of Integer, Integer), ByVal tupleB As Tuple(Of Integer, Integer)) As Integer ' Compare the first Item of each tuple in ascending order. Dim part1 As Integer = tupleA.Item1 Dim part2 As Integer = tupleB.Item1 Dim compareResult As Integer = part1.CompareTo(part2) ' If not equal, return the comparison result. If compareResult <> 0 Then Return compareResult End If ' Compare the second item of each tuple in descending order. Return tupleB.Item2.CompareTo(tupleA.Item2) End Function Sub Main() Dim data As List(Of Tuple(Of Integer, Integer)) = GetData() data.Sort(New Comparison(Of Tuple(Of Integer, Integer))(AddressOf ComparisonTwoTuples)) For Each value In data Console.WriteLine("SORTED ON 2 VALUES: {0}", value) Next End Sub End Module

SORTED ON 2 VALUES: (10, 2) SORTED ON 2 VALUES: (10, 1) SORTED ON 2 VALUES: (100, 2) SORTED ON 2 VALUES: (100, 1)

Optimization, SortedSet. Sort() is sometimes a slow part of a program. There is a way to avoid calling Sort: we can keep the data sorted as we go along. Consider SortedSet.

Version 1 We create a List, add 3 elements to it, and then call Sort. The List is sorted in-place.

Version 2 This code creates a SortedSet, and when we call Add(), each item is stored in a sorted order—we never need to call Sort.

Result It is faster to use the SortedSet. Avoiding Sort altogether seems to be a consistent performance boost.

Module Module1 Sub Main() Dim m As Integer = 100000 Dim s1 As Stopwatch = Stopwatch.StartNew ' Version 1: add 3 strings to List, then Sort it. For i As Integer = 0 To m - 1 Dim list = New List(Of String) list.Add("zebra") list.Add("20") list.Add("bird") list.Sort() If list.Count <> 3 Then Return End If Next s1.Stop() Dim s2 As Stopwatch = Stopwatch.StartNew ' Version 2: add 3 strings to SortedSet. For i As Integer = 0 To m - 1 Dim sorted = New SortedSet(Of String) sorted.Add("zebra") sorted.Add("20") sorted.Add("bird") If sorted.Count <> 3 Then Return End If Next s2.Stop() Dim u As Integer = 1000000 Console.WriteLine(((s1.Elapsed.TotalMilliseconds * u) / m).ToString("0.00 ns")) Console.WriteLine(((s2.Elapsed.TotalMilliseconds * u) / m).ToString("0.00 ns")) End Sub End Module

405.52 ns List, Sort 357.17 ns SortedSet

Summary. Sorting strings can be done in many ways. Here we examined ways to sort strings in alphabetical order, and also reverse alphabetical order. Built-in functions are well-tested.