checking equality of multi-dimensional arrays

Duane

14y2.1kGeneral

Would the following code be the correct way to check for equality between 2 multidimensional arrays?

rivate Function AreArraysEqual(Of T)(ByVal a(,) As T, ByVal b(,) As T) As Boolean

If a Is Nothing AndAlso b Is Nothing Then

Return False

End If

If a Is Nothing Or b Is Nothing Then

Return False

End If

For i As Integer = 0 To a.GetUpperBound(0)

For j As Integer = 0 To a.GetUpperBound(1)

If Not a(i, j).Equals(b(i, j)) Then

Return False

End If

Return True

4 Replies

Know the answer? Post it — somebody with the same question will find it here.

Vulpes14y ago
Here are some examples of using the function:

Imports System

Class Test

Shared Sub Main()

Dim t As New Test
Dim areEqual As Boolean

Dim a As Integer(,) = { {1, 2, 3}, {4, 5, 6} }
Dim b As Integer(,) = { {1, 2, 3}, {4, 5, 6} }
areEqual = t.AreArraysEqual(a, b)
Console.WriteLine("It's '{0}' that a and b are equal", areEqual)

Dim c As Integer(,) = { {11, 22, 33}, {4, 5, 6} }
areEqual = t.AreArraysEqual(a, c)
Console.WriteLine("It's '{0}' that a and c are equal", areEqual)

Dim d As Integer(,) = { {1, 2}, {4, 5} }
areEqual = t.AreArraysEqual(a, d)
Console.WriteLine("It's '{0}' that a and d are equal", areEqual)

Console.ReadKey

End Sub

Private Function AreArraysEqual(Of T)(ByVal a(,) As T, ByVal b(,) As T) As Boolean

If a Is Nothing OrElse b Is Nothing Then
Return False
End If
If (a.GetUpperBound(0) <> b.GetUpperBound(0)) OrElse (a.GetUpperBound(1) <> b.GetUpperBound(1)) Then
Return False
End If
For i As Integer = 0 To a.GetUpperBound(0)
For j As Integer = 0 To a.GetUpperBound(1)
If Not a(i, j).Equals(b(i, j)) Then
Return False
End If
Next
Next
Return True

End Function

End Class
Duane14y ago
I have been unable to check whether the above code works because I'm not sure how to use the result (or even if there is one). I'm afraid I am just not very used to dealing with Functions as opposed to Subs. Sorry for my ignorance. Further help is requested.
Duane14y ago
Thanks for the clarification and definition. That first If-Then statement did appear to be superfluous to me as well (I got most of the function from the web). I'll now check to make sure it works within my program.
Vulpes14y ago
Yes, that generic method is attempting to check for equality of two two-dimensional zero-based arrays.

However, it will throw an exception if the upper bound of 'b' is less than the upper bound of 'a' when attempting to access b(i,j) for indices which don't exist in that array.

To avoid that you need to check that the upper bounds are equal before iterating through the elements.

Also the first 'If' statement is superfluous since if 'a' and 'b' are Nothing, then certainly 'a' is Nothing. However, the 'Or' operator in the second 'If' statement should be replaced with 'OrElse' to avoid unnecessarily checking that 'b' is Nothing if 'a' is Nothing.

Making these changes, leaves us with the following:

Private Function AreArraysEqual(Of T)(ByVal a(,) As T, ByVal b(,) As T) As Boolean

If a Is Nothing OrElse b Is Nothing Then
Return False
End If
If (a.GetUpperBound(0) <> b.GetUpperBound(0)) OrElse (a.GetUpperBound(1) <> b.GetUpperBound(1)) Then
Return False
End If
For i As Integer = 0 To a.GetUpperBound(0)
For j As Integer = 0 To a.GetUpperBound(1)
If Not a(i, j).Equals(b(i, j)) Then
Return False
End If
Next
Next
Return True

End Function