Error when creating dynamic two dimensional array in vb.net

Question

I am trying to increase the x value of the 2 dimensional array but I keep receiving this error.

'ReDim' can only change the rightmost dimension

I need to do this while maintaining the data of the array. Here is my code.

            Dim x As Integer = 0
            Dim y As Integer = 0
            While reader.Read()
                ReDim Preserve catagoryInfo(x, 2)
                catagoryInfo(x, y) = reader.GetString(0)
                y += 1
                catagoryInfo(x, y) = reader.GetString(1)
                x += 1
                y = 0
            End While

Steve · Accepted Answer · 2012-10-30 22:26:50Z

3

In a multidimensional array, you can change only the last dimension when you use Preserve. If you attempt to change any of the other dimensions, a run-time error occurs. A part from this your code is really suboptimal because you are planning to Redim you array at every loop. Redimming with preserve is worse because not only the runtime allocates a new array but it should also copy from the old array to the new array.

In your case is better to declare a simple class like this

Public Class CategoryInfo
    Public info1 As String
    Public info2 As String
End Class

then use a List(Of CategoryInfo)

Dim infos as List(Of CategoryInfo) = new List(Of CategoryInfo)()
While reader.Read()
    Dim nf As CategoryInfo = new CategoryInfo() 
    nf.info1 = reader.GetString(0)
    nf.info2 = reader.GetString(1)
    infos.Add(nf)
    ' if you like the all-in-one-line coding style you could also write the above in this way
    ' infos.Add(New CategoryInfo With {.info1=reader.GetString(0), .info2=reader.GetString(1)} )
End While

Now, if you really need to have your data inside a string array you could write

Dim categoryInfo(infos.Count, 2) as String
for x = 0 to infos.Count -1
    categoryInfo(x,0) = infos(x).info1
    categoryInfo(x,1) = infos(x).info2
next

this is still not very optimal because you loop two times on your data but, at least, it will get your data as you want.

edited Oct 30, 2012 at 22:26

answered Oct 30, 2012 at 22:07

Steve

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5 Comments

spkelly86 Over a year ago

Thanks I'll give it a shot. Still familiarizing myself with the data flow in vb.net. Would it be fine to pass a list through a function or should I even bother converting it to an array?

Steve Over a year ago

Well, arrays have their value. They are very fast to get data from when you know the index. But I advise you to familiarize with Lists and other collections available in the Framework (Dictionary, Hashtable, etc). Of course you could pass a List(Of yourType) to every function or sub you like.

spkelly86 Over a year ago

great! works perfectly. sent the list to the function and it works perfectly. I'd upvote it if i could :)

Steve Over a year ago

Glad to be of help. Remember to accept the answer when the site will allow you

MarkJ Over a year ago

+1. The advice to use List s of objects rather than 2D arrays is life-transforming

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