How to compare and get differences between 2 arrays in EXCEL VBA?

When you’d like to compare 2 arrays in EXCEL VBA whether they are equal or not, what would you do? Furthermore, you might get different elements that don’t overlap each other. I’d like to describe the code that how to get differences of 2 arrays.

At first, you would have to check whether they are equal each other or not because the difference of equal arrays is empty set. Next, you would have to check whether an array is proper subset of another array or not. At last, you could get difference between 2 arrays.

See formula as below, it is shown all elements of Array1 as “A”, all elements of Array2 as “B” and differences elements from Array1 and Array2 as “A And (not B)”.

The following code compares elements between two set and get number of equal elements with double loop, that means to get intersection of 2 sets.

Option Explicit

Function COMPARE_ARRAY(ByRef Array1() As String, ByRef Array2() As String) As Boolean
    Dim i   As Long
    Dim j   As Long
    Dim k   As Long
    k = 0
    For i = LBound(Array1) To UBound(Array1)
        For j = LBound(Array2) To UBound(Array2)
            If Array1(i) = Array2(j) Then
                k = k + 1
            End If
        Next j
    Next i
    If i = j And i = k Then
        COMPARE_ARRAY = True
    Else
        COMPARE_ARRAY = False
    End If
End Function

Function PROPERSUBSET_ARRAY(ByRef Array1() As String, ByRef Array2() As String) As Boolean
    Dim i   As Long
    Dim j   As Long
    Dim k   As Long
    k = 0
    For i = LBound(Array1) To UBound(Array1)
        For j = LBound(Array2) To UBound(Array2)
            If Array1(i) = Array2(j) Then
                k = k + 1
            End If
        Next j
    Next i
    If k = i Then
        PROPERSUBSET_ARRAY = True
    Else
        PROPERSUBSET_ARRAY = False
    End If
End Function

Configuration of the 3rd argument “Compare” specifies which array should be excepted, when it was TRUE the function would except the latter from the former, when it was FALSE then it would except the former from the latter, respectively. It’s assumed that the elements of arrays has no empty string.

Function EXCEPT_ARRAY(ByRef Array1() As String, ByRef Array2() As String, ByVal Compare As Boolean) As String()
    Dim i               As Long
    Dim j               As Long
    Dim k               As Long
    Dim InternalAr1()   As String
    Dim InternalAr2()   As String
    Dim Ar1Ar()         As String
    Dim Ar2Ar()         As String
    InternalAr1 = Array1
    InternalAr2 = Array2
    For i = LBound(InternalAr1) To UBound(InternalAr1)
        For j = LBound(InternalAr2) To UBound(InternalAr2)
            If InternalAr1(i) = InternalAr2(j) Then
                InternalAr1(i) = ""
                InternalAr2(j) = ""
                k = k + 1
            End If
        Next j
    Next i
    k = 0
    For i = LBound(InternalAr1) To UBound(InternalAr1)
        If InternalAr1(i) = "" Then
        Else
            ReDim Preserve Ar1Ar(k)
            Ar1Ar(k) = InternalAr1(i)
            k = k + 1
        End If
    Next i
    k = 0
    For j = LBound(InternalAr2) To UBound(InternalAr2)
        If InternalAr2(j) = "" Then
        Else
            ReDim Preserve Ar2Ar(k)
            Ar2Ar(k) = InternalAr2(j)
            k = k + 1
        End If
    Next j
    If Compare Then
        EXCEPT_ARRAY = Ar1Ar
    Else
        EXCEPT_ARRAY = Ar2Ar
    End If
End Function

REFERENCE:
How to get first cell which is referred to formula and last cell which refers to formula in Excel worksheet?