hiding rows if data is not present in another worksheet - vba

Question

I have about 34,000 lines of data in a worksheet and I need too hide rows that does not have matching data in another worksheet. I have some code but i seems to hide all the data instead of jst hiding the data which is not represented in the other worksheet. The code is shown below and any help would be appreciated!
Sub HideCells()
Dim xlRange As Range
Dim xlCell As Range
Dim xlSheet As Worksheet, sht As Worksheet
Dim valueToFind
Dim i As Long, lastrow As Long, lastrow2 As Long
Set xlSheet = ActiveWorkbook.Worksheets("Køb VT nummer")
lastrow = xlSheet.Cells(xlSheet.Rows.Count, "A").End(xlUp).Row
Set xlRange = xlSheet.Range("A1:A" & lastrow)
Set sht = ActiveWorkbook.Worksheets("køb total")
lastrow2 = sht.Cells(sht.Rows.Count, "A").End(xlUp).Row
Debug.Print lastrow
Debug.Print lastrow2
For i = 2 To lastrow2
valueToFind = Sheets("køb total").Cells(i, 7).Value
For Each xlCell In xlRange
If Not xlCell.Value = valueToFind Then
Worksheets("Køb total").Rows(i).EntireRow.Hidden = True
Exit For
End If
Next xlCell
Next i
End Sub

Answer 1

This is because a line containing "ValueToFind" for one value of "i" doesn't necessarily contain it for a different value of "i"
Try
Worksheets("Køb total").usedRange.rows.hidden = true
For i = 2 To lastrow2
valueToFind = Sheets("køb total").Cells(i, 7).Value
For Each xlCell In xlRange
If xlCell.Value = valueToFind Then
Worksheets("Køb total").Rows(i).EntireRow.Hidden = False
End If
Next xlCell
Next i

Answer 2

Your code will run much faster if you do all the hiding at the end of the checking.
Sub HideCells()
Dim xlRange As Range
Dim xlCell As Range
Dim xlSheet As Worksheet, sht As Worksheet
Dim i As Long, lastrow As Long, lastrow2 As Long
Dim rngHide As Range, c As Range
Set xlSheet = ActiveWorkbook.Worksheets("Køb VT nummer")
lastrow = xlSheet.Cells(xlSheet.Rows.Count, "A").End(xlUp).Row
Set xlRange = xlSheet.Range("A1:A" & lastrow)
Set sht = ActiveWorkbook.Worksheets("køb total")
lastrow2 = sht.Cells(sht.Rows.Count, "A").End(xlUp).Row
For Each c In sht.Range("G2:G" & lastrow2)
'any match on the other sheet?
If IsError(Application.Match(c.Value, xlRange, 0)) Then
If rngHide Is Nothing Then
Set rngHide = c
Else
Set rngHide = Application.Union(rngHide, c)
End If
End If
Next c
'any rows to hide? If Yes then hide them all
If Not rngHide Is Nothing Then rngHide.EntireRow.Hidden = True
End Sub