Compare two sheets using arrays

Question

My code is super slow (10+ min for each sheet) due to the quantity of data i have. I believe there may be a way to speed it up using arrays, but i am not sure how to go abo

Answer 1

Welcome to SO. Great question. Give this procedure a shot. You could probably tidy it up a bit, but it should work and be significantly faster.

For reference, see this link.

Update: I tested this on two randomly generated data sets of 10K and 11K rows. It took less than a blink of an eye. I didn't even have time to look at see the time when I started.

Option Explicit

Private Sub cmdCompare2to1_Click()

Dim sheet1 As Worksheet, sheet2 As Worksheet, sheet3 As Worksheet
Dim lngLastR As Long, lngCnt As Long
Dim var1 As Variant, var2 As Variant, x
Dim rng1 As Range, rng2 As Range


Set sheet1 = Worksheets(1)
Set sheet2 = Worksheets(2)
Set sheet3 = Worksheets(3) ' assumes sheet3 is a blank sheet in your workbook

Application.ScreenUpdating = False

'let's get everything all set up
'sheet3 column headers
sheet3.Range("A1:B1").Value = Array("in1Not2", "in2Not1")

'sheet1 range and fill array
With sheet1

    lngLastR = .Range("A" & .Rows.Count).End(xlUp).Row

    Set rng1 = .Range("A1:A" & lngLastR)
    var1 = rng1

End With

'sheet2 range and fill array
With sheet2

    lngLastR = .Range("A" & .Rows.Count).End(xlUp).Row

    Set rng2 = .Range("A1:A" & lngLastR)
    var2 = rng2

End With

'first check sheet1 against sheet2
On Error GoTo NoMatch1
For lngCnt = 1 To UBound(var1)

    x = Application.WorksheetFunction.Match(var1(lngCnt, 1), rng2, False)

Next


'now check sheet2 against sheet1
On Error GoTo NoMatch2
For lngCnt = 1 To UBound(var2)

    x = Application.WorksheetFunction.Match(var2(lngCnt, 1), rng1, False)

Next

On Error GoTo 0
Application.ScreenUpdating = True
Exit Sub

NoMatch1:
    sheet3.Range("A" & sheet3.Rows.Count).End(xlUp).Offset(1) = var1(lngCnt, 1)
    Resume Next


NoMatch2:
    sheet3.Range("B" & sheet3.Rows.Count).End(xlUp).Offset(1) = var2(lngCnt, 1)
    Resume Next


End Sub