Speed up VBA marco - vba

Question

I have a macro that does work, it's just really slow when there is a lot of data and I'm hoping that someone on here can help me to speed it up.
When my VBA does is check the columns of a sheet for the value "NULL" and if it's there it clears that cell. Here's the code:
Sub RemoveNullColumn()
Dim c, count, r, lc, FirstCell
Application.ScreenUpdating = False
count = 0
r = ActiveCell.row 'lets you choose where you want to start even if it is not at "A1"
c = ActiveCell.Column 'lets you choose where you want to start even if it is not at "A1"
c = GetLetterFromNumber(c) 'Gets the column letter from the number provided above
FirstCell = c & r 'sets the cell that you selected to start in so that you will end thereafter removing all the NULL
lc = ActiveSheet.Cells(1, Columns.count).End(xlToLeft).Column 'Finding the last used column
For H = ActiveCell.Column To lc Step 1 'Starts with where you selected a cell and moves right to the last column
For x = 1 To Range(c & Rows.count).End(xlUp).row Step 1 'Starts with the first row and moves through the last row
count = count + 1
If Range(c & x).Value = "NULL" Then 'Checks the contents fo the cell to see if it is "NULL"
Range(c & x).Clear
End If
If count = 1000 Then 'This was used testing but is not seen with the ScreenUpdating set to false
Range(c & x).Select
count = 1
End If
Next x
ActiveCell.Offset(0, 1).Select 'select the next column
c = ActiveCell.Column
c = GetLetterFromNumber(c) 'get the letter of the next column
Next H
Application.ScreenUpdating = True
MsgBox "Finished"
Range(FirstCell).Select
End Sub
Function GetLetterFromNumber(Number)
GetLetterFromNumber = Split(Cells(1, Number).Address(True, False), "$")(0)
End Function
When there are not a lot of rows it is pretty fast, but there are a lot of rows it is slow.
I have a file that I ran it on that has columns from A to AD and 61k+ rows, it took more than 30 minutes to finish and I'm hoping to make that much faster.

Answer 1

Instead of looking into Every single cell in the worksheet, use Replace function which is far faster :(you may need to edit it customize it to your needs)
Example :
Sub RemoveNullColumn()
Dim targetSheet As Worksheet
Set targetSheet = ActiveSheet 'TODO: replace with a stronger object reference
targetSheet.Cells.Replace What:="NULL", Replacement:="", LookAt:=xlWhole, _
SearchOrder:=xlByRows, MatchCase:=False, SearchFormat:=False, _
ReplaceFormat:=False
End Sub
This will make sure you will preserve the format.

Answer 2

If you want to clear NULL using ActiveCell as reference:
Range(ActiveCell, Selection.End(xlToRight)).Select
Range(Selection, Selection.End(xlDown)).Select
Selection.Replace What:="NULL", Replacement:="", LookAt:=xlPart, _
SearchOrder:=xlByRows, MatchCase:=True, SearchFormat:=False, _
ReplaceFormat:=False

Answer 3

Please give this a try...
Sub RemoveNullColumn()
Dim lr As Long, lc As Long
Dim rng As Range, cell As Range, FirstCell As Range
With Application
.Calculation = xlCalculationManual
.EnableEvents = False
.ScreenUpdating = False
End With
lr = Cells.Find("*", SearchOrder:=xlByRows, SearchDirection:=xlPrevious).Row
lc = Cells.Find("*", SearchOrder:=xlByColumns, SearchDirection:=xlPrevious).Column
Set FirstCell = ActiveCell
Set rng = Range(Cells(1, FirstCell.Column), Cells(lr, lc))
For Each cell In rng
If cell.Value = "NULL" Then
cell.Clear
End If
Next cell
With Application
.Calculation = xlCalculationAutomatic
.EnableEvents = True
.ScreenUpdating = True
End With
MsgBox "Finished"
End Sub

Answer 4

Use a .Find/.FindNext to collect all of the matching cells into a Union then clear the contents of the Union'ed cells.
Option Explicit
Sub noNULLs()
Dim firstAddress As String, c As Range, rALL As Range
With ActiveSheet.Cells 'This should be named worksheet like Worksheets("sheet1")
Set c = .Find("NULL", MatchCase:=True, _
LookIn:=xlValues, LookAt:=xlWhole)
If Not c Is Nothing Then
Set rALL = c
firstAddress = c.Address
Do
Set rALL = Union(rALL, c)
Set c = .FindNext(c)
Loop While c.Address <> firstAddress
rALL.Clear
End If
End With
End Sub