VBA code too slow - takes 6 hours to execute output - excel

Question

I have a lengthy code unable to share the 8000+ liner code completely, The code runs through loops multiple times row by row, if there are 10000+ rows then loop runs 10000+ times.
Since the code is too lengthy I am sharing a part of it were I feel it can shorten the time taken, But I am missing a loop in it and how do I include that Is my query for now.
I’ll be sharing the original code and very next is the replacement code kindly check and let me know we’re and how to include.
Original code:
For i = 2 To endlineMM
If worksheets(“MM Source”).cells(I,9).value = “registered locked” or worksheets(“MM Source”).cells(i,9).value = “registered unlocked” Then
For j = 3 to endlineDHDO
If instr(Lcase(worksheets(“DHDO”).cells(j,2).value),Lcase(Worksheets(“MM Source”).cells(i,2).value)) <> 0 Then
If Lcase(Worksheets(“MM Source”).cells(i,2).value) = Lcase(worksheets(“DHDO”).cells(j,2).value) Then
Found missing = True
Exit For
Else if j= EndlineDHDO And Lcase(Worksheets(“MM Source”).cells(i,2).value)<>
Lcase(worksheets(“DHDO”).cells(j,2).value) Then
Foundmissing = false
End if
Next j
If foundmissing = False Then
Etc......
Replacement code:
For i = 2 to endlineMM
If worksheets(“MM Source”).cells(I,9).value = “registered locked” or worksheets(“MM Source”).cells(i,9).value = “registered unlocked” Then
Test_ID = Worlsheets(“MM Source”).cells(i,2).value
With sheets(“DHDO”).Range(“B:B“)
Set prg = .Find(Test_ID, LookIn:=xlvalues)
If prg is nothing then
Foundmissing =true
Exit for
Else
Foundmissing = false
End if
End with
If foundmissing = false Then
Etc......
If you observe above from original code it has “i“ as well as “j” but in replacement code I am missing “j”
How can I fix my Replacement code
let me know how to edit the Replacement code please

Answer 1

Generally speaking, your code will run a lot faster if you use Ranges and Arrays rather than individual Cells.
For example, if you were to take a spreadsheet and fill columns A1:B10000, with numeric data, and then compare the performance of the two following codes:
Dim data As Variant
Dim output(10000) As Double
Dim i As Integer
data = Application.Transpose(Application.Transpose(Range("A1", "B10000")))
For i = 1 To 10000
output(i - 1) = data(i, 1) + data(i, 2)
Next
Range("C1", "C10000").Value = Application.Transpose(output)
and
Dim i As Integer
For i = 1 To 10000
Cells(i, 3).Value = Cells(i, 1).Value + Cells(i, 2).Value
Next
You will notice that the first variation is considerably faster.
By way of explanation Application.Transpose is necessary to assign the range to an array. It needs to be doubled in the first case, because it is a two-dimensional array.

Answer 2

Here is a sample that will filter the MM Source sheet, then loop through the visible cells finding cells in DHDO sheet
Sub Do_It()
Dim sh As Worksheet, ws As Worksheet
Dim rng As Range, c As Range
Dim a As Range
Set sh = Sheets("MM Source")
Set ws = Sheets("DHDO")
Application.ScreenUpdating = False
With sh
Set rng = .Range("I2:I" & .Cells(.Rows.Count, "I").End(xlUp).Row)
.Columns("I:I").AutoFilter Field:=1, Criteria1:= _
"=registered locked", Operator:=xlOr, Criteria2:="=registered unlocked"
For Each c In rng.SpecialCells(xlCellTypeVisible).Cells
Set a = ws.Range("B:B").Find(c.Offset(, -7), LookIn:=xlValues)
If Not a Is Nothing Then
'MsgBox "Do nothing"
Else
'MsgBox "Do something"
c.Interior.Color = vbGreen
End If
Next c
.AutoFilterMode = False
End With
End Sub