checking equality of multi-dimensional arrays

Question

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

Vulpes · Answer

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

Duane · Answer

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.

Duane · Answer

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.

Vulpes · Answer

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(ij) 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