Arrays - Miscellaneous Methods

Arrays

Miscellaneous Methods

VB.NET has introduced some very powerful methods for arrays. We will review some of these functions in this lesson.

Array.IndexOf and Array.LastIndexOf

Array.IndexOf returns the index of the first occurrence of a value in a one-dimensional array. Array.LastIndexOf returns the index of the last occurrence of a value in a one-dimensional array. These methods provide another way of locating a value in an array.

The syntax for each method, respectively, is:

Position = Array.IndexOf(Array, ValueToFind)

and

Position = Array.LastIndexOf(Array, ValueToFind)

where Array is the one-dimensional array to search, ValueToFind is the value that you are looking for, and Position is the index in the array where the item was found. If the item is not found, the value of Position will be -1.

Sample program:

VB Code:

Screen-shot of run:

Module Module1

Sub Main()

Dim aintNumbers() As Integer = {12, 23, 44, 15, 46, 27, 18, 12}

Dim intX As Integer

Dim intPosition As Integer

Console.WriteLine("Array contents:")

Console.WriteLine()

For intX = 0 To UBound(aintNumbers)

Console.Write(aintNumbers(intX) & " ")

Console.WriteLine()

intPosition = Array.IndexOf(aintNumbers, 12)

Console.WriteLine("Index of 12: " & intPosition)

Console.WriteLine()

intPosition = Array.LastIndexOf(aintNumbers, 12)

Console.WriteLine("Last Index of 12: " & intPosition)

Console.WriteLine()

Console.WriteLine("Press Enter to close this window.")

Console.ReadLine()

End Sub

End Module

You can download the code here.

Array.Copy

The Array.Copy method copies one array (or a section of an array) to another array. The syntax is:

Array.Copy(SourceArray, DestinationArray, NumberOfItemsToCopy)

- or -

Array.Copy(SourceArray, SourceStartIndex, DestinationArray, DestinationStartIndex, NumberOfItemsToCopy))

Sample program:

VB Code:

Screen-shot of run:

Module Module1

Sub Main()

Dim aintSource() As Integer = {12, 23, 44, 15, 46, 27, 18, 12}

Dim aintDest(4)

Dim intX As Integer

Console.WriteLine("Source Array contents:")

For intX = 0 To UBound(aintSource)

Console.Write(aintSource(intX) & " ")

Console.WriteLine()

Array.Copy(aintSource, aintDest, 5)

Console.WriteLine()

Console.WriteLine("Destination Array contents after copying 5 elements:")

For intX = 0 To UBound(aintDest)

Console.Write(aintDest(intX) & " ")

Console.WriteLine()

Console.WriteLine("Press Enter to close this window.")

Console.ReadLine()

End Sub

End Module

You can download the code here.

Distinct

The Distinct method finds all the unique values in the source array and copies them to the destination array. The syntax is:

DestinationArray = SourceArray.Distinct.ToArray

Sample program:

VB Code:

Screen-shot of run:

Module Module1

Private maintRandomNumbers(9) As Integer

Private maintDisctinctValues() As Integer

Sub Main()

PopulateArray()

maintDisctinctValues = maintRandomNumbers.Distinct.ToArray

Console.WriteLine("The distinct numbers are:")

For intX = 0 To UBound(maintDisctinctValues)

Console.Write(CStr(maintDisctinctValues(intX)).PadLeft(5))

Console.WriteLine()

Console.WriteLine("Press Enter to close this window.")

Console.ReadLine()

End Sub

Private Sub PopulateArray()

Dim intX As Integer

Console.WriteLine("The numbers generated are:")

Randomize()

For intX = 0 To 9

maintRandomNumbers(intX) = GetRandomNumber(1, 10)

Console.Write(CStr(maintRandomNumbers(intX)).PadLeft(5))

Console.WriteLine()

End Sub

Private Function GetRandomNumber(ByVal pintLowerBound As Integer, _

ByVal pintUpperBound As Integer) _

As Integer

' This function will return a random integer that falls within

' the range of the two arguments passed.

Return Int((pintUpperBound - pintLowerBound + 1) * Rnd() _

+ pintLowerBound)

End Function

End Module

You can download the code here.