Something to play with...

Function StripDupes(Optional AllowDupes As Boolean = True) As Boolean
' Compares colA to colB and removes colA matches found in colB.
' Args In: AllowDupes: True by default
' Keeps duplicate values found in colA that are not found
in colB;
' If False, duplicate values in colA not found in colB are
removed.
'
' Returns: True if matches are found --AND-- no error occurs;
' False if matches are NOT found --OR-- error occurs.
'
' Sources: Ron Rosenfeld, Jim Cone, Garry Sansom

Dim i&, j&, lRows1&, lRows2&, lMatchesFound& 'as long
Dim vRngA, vRngB, vRngOut() 'as variant
Dim dRngB As New Dictionary

On Error GoTo ErrExit

lRows1 = Cells(Rows.Count, "A").End(xlUp).Row
lRows2 = Cells(Rows.Count, "B").End(xlUp).Row
vRngA = Range("A1:A" & lRows1): vRngB = Range("B1:B" & lRows2)

For j = LBound(vRngB) To UBound(vRngB)
With dRngB
If Not .Exists(Key:=vRngB(j, 1)) Then _
.Add Key:=vRngB(j, 1), Item:=vRngB(j, 1)
End With
Next 'j

If AllowDupes Then '//fastest
For i = LBound(vRngA) To UBound(vRngA)
If dRngB.Exists(Key:=vRngA(i, 1)) Then _
vRngA(i, 1) = "": lMatchesFound = lMatchesFound + 1
Next 'i

j = 0: ReDim vRngOut(UBound(vRngA) - lMatchesFound, 0)
For i = LBound(vRngA) To UBound(vRngA)
If Not vRngA(i, 1) = "" Then _
vRngOut(j, 0) = vRngA(i, 1): j = j + 1
Next 'i

Else '//slowest
Dim dRngA As New Dictionary
For i = LBound(vRngA) To UBound(vRngA)
If Not dRngB.Exists(vRngA(i, 1)) Then
With dRngA
If Not .Exists(Key:=vRngA(i, 1)) Then _
.Add Key:=vRngA(i, 1), Item:=vRngA(i, 1)
End With 'dRngA
End If 'Not dRngB.Exists(vRngA(i, 1))
Next 'i

Dim v As Variant
j = 0: ReDim vRngOut(dRngA.Count, 0)
For Each v In dRngA
vRngOut(j, 0) = dRngA(v): j = j + 1
Next 'v
End If 'AllowDupes

Range("A1:A" & lRows1).ClearContents
Range("A1").Resize(UBound(vRngOut), 1) = vRngOut

ErrExit:
StripDupes = (Err = 0)
End Function 'StripDupes()

--
Garry

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