Flatten array. It can be difficult to use 2D arrays in VB.NET programs. Sometimes it is helpful to flatten these arrays into 1D arrays.

2D Array

Array

By looping over all the values in the upper bounds of the array for each rank, we can copy elements to a 1D array. In VB.NET this can be done with nested For To loops and GetUpperBound.

Example. In the Main subroutine, we create a 2D array with 2 rows and 3 columns. Our goal is to convert this to a flattened array of 6 elements.

Array Length

For

Module Module1

    Function Flatten(input As Integer(,)) as Integer()
        ' Step 1: if zero elements, return an empty array.
        If input.Length = 0
            Return {}
        End If

        ' Step 2: get total element count, and allocate the 1D array.
        Dim resultInteger(input.Length - 1) As Integer

        ' Step 3: use nested For-loops with GetUpperBound to copy all elements.
        Dim write = 0
        For i = 0 To input.GetUpperBound(0)
            For z = 0 To input.GetUpperBound(1)
                resultInteger(write) = input(i, z)
                write += 1
            Next
        Next

        ' Step 4: return the 1D array.
        Return resultInteger
    End Function

    Sub Main()
        Dim elements = { { 10, 20, 30 }, { 40, 50, 60 } }

        ' Call Flatten.
        Dim result = Flatten(elements)
        For Each value in result
            Console.WriteLine("ELEMENT: {0}", value)
        Next
    End Sub
    
End Module
ELEMENT: 10
ELEMENT: 20
ELEMENT: 30
ELEMENT: 40
ELEMENT: 50
ELEMENT: 60

Sometimes the dimensions of a 2D array are not useful—the values themselves may be the important part. We could still average the elements, for example.

In this case, flattening the array is worthwhile. Other Functions in the VB.NET program may be better able to deal with the flattened one-dimensional array.