How to speed up the comparision of 2 collections in VBA? - excel

Question

I have written a macro that gets a collection of collection and than takes two of the collections and gives me the similarity.
Now if I compare the two collections with a simple for loop it will take hours to compare all 854 collection that are contained in pCol.
Here is my code:
Function CompareCollections(ByVal pCol As Collection) As Collection
Dim outer As Long
Dim inner As Long
'collections that will be compared to each other
Dim inCol As Collection
Dim outCol As Collection
'collection used for return values
Dim retCol As Collection
'result of single comparison
Dim res As CompResult
'comparison variables
Dim iIdx As Long
Dim oIdx As Long
Dim same As Long
Set retCol = New Collection
For outer = 1 To pCol.Count - 1
Set outCol = pCol(outer)
For inner = outer + 1 To pCol.Count
Set inCol = pCol(inner)
Set res = New CompResult
res.LeftTable = outCol(1) 'index 1 contains a header
res.RightTable = inCol(1)
'compare the two collections <== PART I WANT TO SPEED UP
same = 0
For oIdx = 2 To outCol.Count 'starting with 2 to ignore the header
For iIdx = 2 To inCol.Count
If inCol(iIdx) = outCol(oIdx) Then same = same + 1
Next iIdx
DoEvents
Next oIdx
res.Result1 = same / (outCol.Count - 1)
res.Result2 = same / (inCol.Count - 1)
retCol.Add res
Set res = Nothing
Set inCol = Nothing
DoEvents
Next inner
Set outCol = Nothing
DoEvents
Next outer
Set CompareCollections = retCol
End Function
I really hope you guys can help me.
EDIT:
The CompResult class is a simple structure, because I could not add a custom type to the collection:
Private mLeftTable As String
Private mRightTable As String
Private mResult1 As Double
Private mResult2 As Double
Public Property Get LeftTable() As String
LeftTable = mLeftTable
End Property
Public Property Let LeftTable(value As String)
mLeftTable = value
End Property
Public Property Get RightTable() As String
RightTable = mRightTable
End Property
Public Property Let RightTable(value As String)
mRightTable = value
End Property
Public Property Get Result1() As Double
Result = mResult1
End Property
Public Property Let Result1(value As Double)
mResult1 = value
End Property
Public Property Get Result2() As Double
Result = mResult2
End Property
Public Property Let Result2(value As Double)
mResult2 = value
End Property

Answer 1

A first tip: try to precalculate outCol.Count, inCol.Count and pCol.Count in order to avoid unnecessary calculations.
Second tip: if in your object CompResult the res.Result1 and res.Result2 are integers, use "\" instead of "/".
Third tip: try to use integers instead of long values wherever you can.
Fourth tip: try to replace for loops by a "for each" loops when looping for every column. It seems a little faster.
A last tip might be transform collections (ranges) in arrays and iterate through them, as it seems faster than iterate through ranges.