Dynamic Multi-Dimensional array problem

Question

I have this code:

Module Module1
    Dim x As Integer = 1
    Dim y As Integer = 1
    Dim arr(x, y) As String

    Sub Main()
        x += 2
        y += 3

        For ix = 0 To x
            For iy = 0 To y
                arr(ix, iy) = String.Format("{0}:{1}", ix, iy)
            Next
        Next

        For ix = 0 To x
            For iy = 0 To y
                Console.WriteLine(arr(ix, iy))
            Next
        Next

        Console.Read()
    End Sub

End Module

And with it I'm trying to change the upper bound of array dimensions. But I get this error:"Index was outside the bounds of the array". What I'm doing wrong?

msarchet · Accepted Answer · 2011-06-14 14:52:07Z

3

You can't change the upper-bound of an array like that in .NET. If you need a dynamically sized Array I'd suggest looking at List as it allows you to do all of this.

You'll want to do something like:

Dim yourStrings AS List(Of List(Of String)) = New List(Of New List(Of String)

To convert this to a 2-D Array:

Dim maxListLength As Integer = 0
For Each subList In yourStrings
    maxListLength = If(subList.Length > maxListLength, subList.Length, maxListLength)
Next

Dim yourArray(yourString.Length - 1, maxListLength -1) As String

Dim x As Integer = 0
Dim y As Integer = 0

For Each subList In yourString
    For Each str In subList
        yourArray(x, y) = str
        y = y + 1
    Next
    x = x + 1
Next

From 2-D to List(Of List(Of String))

Dim yourList As List(Of List(Of String)) = New List(Of List(Of String))

For i = 0 To ArrayXSize
    Dim thisXString = New List(Of String)
    For j = 0 To ArrayYSize
       thisXStrings.Add(yourArray(i,j))
    Next
    yourList.Add(thisXStrings)  
Next

edited Jun 14, 2011 at 14:52

answered Jun 14, 2011 at 14:20

msarchet

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2 Comments

Jon Egerton Over a year ago

+1 Seconded - Even if you need an array afterwards you can just ToArray the list.

Cobold Over a year ago

How can I convert 2-D array to list and then convert the list back to 2-D array?

arthur86 · Accepted Answer · 2011-06-14 14:23:05Z

1

If you declare array with dimension x and y, to use outbound value you have to redim array using redim() command:

MSDN Redim Command Doc

Example:

Dim intArray(10, 10, 10) As Integer
ReDim Preserve intArray(10, 10, 20)

answered Jun 14, 2011 at 14:23

arthur86

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2 Comments

Cobold Over a year ago

I want to be able to change any dimension upper bounds, but ReDim don't allow it.

arthur86 Over a year ago

Yes, redim allow you to redi each dimension ... ReDim Preserve intArray(10, 20, 20) for example modify second and third dimension.

Bala R · Accepted Answer · 2011-06-14 14:22:00Z

0

You can use ReDim to reallocate memory as needed.

answered Jun 14, 2011 at 14:22

Bala R

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Comments

Cobold · Accepted Answer · 2011-06-14 16:15:35Z

0

I made this by myself:

   Private Function MultiReDim(ByVal a As Array, ByVal dimOne As Short, ByVal dimTwo As Short) As String(,)
        Dim newArr(dimOne, dimTwo) As String
        For x = 0 To newArr.GetUpperBound(0)
            For y = 0 To newArr.GetUpperBound(1)
                If x <= a.GetUpperBound(0) AndAlso y <= a.GetUpperBound(1) Then
                    newArr(x, y) = a(x, y)
                Else
                    newArr(x, y) = Nothing
                End If

            Next
        Next

        Return newArr
    End Function

It works with 2D arrays, but can be modified to work with unlimited number of arrays by adding a ParamArray of dimensions.

answered Jun 14, 2011 at 16:15

Cobold

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Comments

Phil Jollans · Accepted Answer · 2017-12-29 17:26:25Z

I don't know when this syntax was introduced, but you can define an array with a dynamic size using:

Dim arr As String(,) = New String(x,y){}

or simply

Dim arr = New String(x,y){}

or using the original example

Module Module1

    Dim x As Integer = 1
    Dim y As Integer = 1
    Dim arr(x, y) As String

    Sub Main()
        x += 2
        y += 3

        arr = New String(x,y){}

        For ix As Integer = 0 To x
            For iy As Integer = 0 To y
                arr(ix, iy) = String.Format("{0}:{1}", ix, iy)
            Next
        Next

        For ix As Integer = 0 To x
            For iy As Integer = 0 To y
                Console.WriteLine(arr(ix, iy))
            Next
        Next

        Console.Read()
    End Sub

End Module

(not tested).

I think this syntax is preferable to the old (VB6 style) ReDim statement.

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