Excel VBA - ArrayList of ArrayLists to Excel Sheet - excel

Question

Looking for a more appropriate approach. I have a working solution, but it seems there should be a built-in or more elegant method.
I am comparing two sheets from separate workbooks, documenting the differences on a sheet in current workbook. Every time a difference is found, I'm generating a row of output data. As I'm unaware of the total number of differences I will find, the row of output data is appended to an ArrayList.
I have a working bit of code, but the effective method is:
Create a row as an arraylist.
Convert the row to an array.
Add the row to an arraylist for output
TWICE Transpose the output arraylist while converting to an array
Output the array to worksheet.
With all the benefit of using ArrayLists, it seems that there should be a direct method for outputting a 2D "ArrayList of ArrayLists" or something along those lines.
Here is the current code:
Sub findUnmatchingCells()
Dim oWB_v1 As Workbook, oWB_v2 As Workbook, oRange_v1 As Range, oRange_v2 As Range
On Error GoTo endofsub
With Me
.Cells.Clear
.Cells(1, 1) = "Row"
.Cells(1, 2) = "Column"
.Cells(1, 3) = "v1"
.Cells(1, 4) = "v2"
End With
Dim missing_items As Object
Dim output_row(), output(), missing_row As Object
Set oWB_v1 = Workbooks("foo.xls")
Set oWB_v2 = Workbooks("bar.xls")
Set oRange_v1 = oWB_v1.Sheets(1).Range("A1:AD102")
Set oRange_v2 = oWB_v2.Sheets(1).Range("A1:AD102")
Set missing_items = CreateObject("System.Collections.ArrayList")
For rRow = 1 To oRange_v1.Rows.Count
For cCol = 1 To oRange_v1.Columns.Count
If oRange_v1.Cells(rRow, cCol) <> oRange_v2.Cells(rRow, cCol) Then
Set missing_row = CreateObject("System.Collections.ArrayList")
missing_row.Add rRow
missing_row.Add cCol
missing_row.Add oRange_v1.Cells(rRow, cCol).Value2
missing_row.Add oRange_v2.Cells(rRow, cCol).Value2
output_row = missing_row.toarray
missing_items.Add output_row
End If
Next cCol
Next rRow
output = Application.WorksheetFunction.Transpose(Application.WorksheetFunction.Transpose(missing_items.toarray))
'my own output routine
If Not outputArrayToRange(output, Me.Range("A2")) Then Stop
Exit Sub
endofsub:
Debug.Print rRow, cCol, missing_items.Count, missing_row.Count, Error
Stop
End Sub

Answer 1

Seems like a lot of extra work here with ArrayList when you are not really using anything useful from them. As you know the mismatch count cannot be more than the number of start elements, and the columns will be 4 at end, you can do all of this just with a single array. Pre-size the array and in your loop populate it.
Simplified example:
As you are using Me this code would be in "Sheet1".
Now it would get more complicated if you wanted to ReDim to actual number of mismatches to avoid over-writing something, but generally it is wise to plan developments to avoid such risks. You would need the double transpose to be able to ReDim the rows as columns then back to rows.
With the ranges you mention I don't think the Transpose limit would be an issue, but that is a concern in other cases which needs to be resolved with additional looping.
The efficient way is to use arrays the whole time. Read the two ranges into arrays, loop one and compare against the other, write out changes to pre-sized array, write array to sheet
If this is just about is there nicer functionality for this within ArrayLists, no. What you have done is short and effective but incurs more overhead than is necessary.
Option Explicit
Public Sub findUnmatchingCells()
Dim oWB As ThisWorkbook, oRange_v1 As Range, oRange_v2 As Range
With Me
.Cells.Clear
.Cells(1, 1) = "Row"
.Cells(1, 2) = "Column"
.Cells(1, 3) = "v1"
.Cells(1, 4) = "v2"
End With
Dim rRow As Long, cCol As Long
Set oWB = ThisWorkbook
Set oRange_v1 = oWB.Worksheets("Sheet2").Range("A1:D3") 'would be faster to read this into array and later loop that
Set oRange_v2 = oWB.Worksheets("Sheet3").Range("A1:D3") 'would be faster to read this into array and later loop that
Dim totalElements As Long, output()
totalElements = oRange_v1.Rows.Count * oRange_v1.Rows.Count
ReDim output(1 To totalElements, 1 To 4)
For rRow = 1 To oRange_v1.Rows.Count 'would be faster to loop arrays than sheet
For cCol = 1 To oRange_v1.Columns.Count
If oRange_v1.Cells(rRow, cCol) <> oRange_v2.Cells(rRow, cCol) Then
output(rRow, 1) = rRow
output(rRow, 2) = cCol
output(rRow, 3) = oRange_v1.Cells(rRow, cCol).Value2
output(rRow, 4) = oRange_v2.Cells(rRow, cCol).Value2
End If
Next cCol
Next rRow
oWB.Worksheets("Sheet1").Cells(2, 1).Resize(UBound(output, 1), UBound(output, 2)) = output
End Sub
Other thoughts:
You can have early bound if adding references is not a concern:
From: https://www.snb-vba.eu/VBA_Arraylist_en.html
ThisWorkbook.VBProject.References.AddFromFile "C:\WINDOWS\Microsoft.NET\Framework\v4.0.30319\mscorlib.tlb"
or
ThisWorkbook.VBProject.References.AddFromguid "{BED7F4EA-1A96-11D2-8F08-00A0C9A6186D}", 2, 4
You are wasting an already created object by continually re-creating your missing_row ArrayList within loop. Create it once, before the loop, and just before you loop round again call the .Clear method.