Removing duplicates in a for loop crashes Excel - arrays

Question

I have a for next loop that runs through a couple hundred thousand lines making changes on most. Could an array to make this code run faster?
The example of my for loop. Sometimes it gets overloaded and crashes Excel. (FYI my loop has to run bottom to top for it to do its intended purpose.)
Sub RemoveDuplicates()
Dim shWorkBook As Worksheet
Dim wkb As Workbook
Dim FullYearData As Worksheet
Set wkb = ThisWorkbook
With wkb
Set shWorkBook = .Sheets("Workbook")
Set shFullYearData = .Sheets("FullYearData")
End With
Dim i As Long
Dim LastRowW As Long
On Error Resume Next
Call TurnOffCalc
FirstRowW = shWorkBook.Cells(1, 1).Row
FirstColW = shWorkBook.Cells(1, 1).Column
LastRowW = shWorkBook.Cells(Rows.Count, 1).End(xlUp).Row
LastColW = shWorkBook.Cells(2, Columns.Count).End(xlToLeft).Column
i = LastRowW
Sum = 0
shWorkBook.Activate
For i = LastRowW To 1 Step -1
If shWorkBook.Cells(i, 7) = shWorkBook.Cells(i - 1, 7) Then
shWorkBook.Cells(i, 26) = vbNullString
End If
If shWorkBook.Cells(i, 26).Value <> "" Then
shWorkBook.Cells(i, 27) = Sum + Cells(i, 25).Value
Sum = 0
ElseIf shWorkBook.Cells(i, 26).Value = "" Then
Sum = shWorkBook.Cells(i, 25).Value + Sum
End If
Next
p = FirstRowW + 1
For p = FirstRowW + 1 To LastRowW Step 1
shWorkBook.Cells(p, 28) = Application.WeekNum(shWorkBook.Cells(p, 3))
Next
shWorkBook.Cells(1, 28).Value = "Week Number"
Call TurnOnCalc
End Sub

Answer 1

Try something like this:
Sub RemoveDuplicates()
Dim shWorkBook As Worksheet
Dim wkb As Workbook
Dim FullYearData As Worksheet
Dim i As Long, Sum
Dim LastRowW As Long, LastColW As Long, tbl As Range, data
Set wkb = ThisWorkbook
With wkb
Set shWorkBook = .Sheets("Workbook")
'Set shFullYearData = .Sheets("FullYearData")
End With
LastRowW = shWorkBook.Cells(Rows.Count, 1).End(xlUp).Row
LastColW = shWorkBook.Cells(2, Columns.Count).End(xlToLeft).Column
Set tbl = shWorkBook.Range("A1").Resize(LastRowW, 28) 'include "Week number" (?)
data = tbl.Value 'get the range value as an array
data(1, 28) = "Week Number"
Sum = 0
For i = LastRowW To 1 Step -1
If data(i, 7) = data(i - 1, 7) Then data(i, 26) = vbNullString
If data(i, 26).Value <> "" Then
data(i, 27) = Sum + data(i, 25).Value
Sum = 0
Else
Sum = data(i, 25).Value + Sum
End If
If i > 1 Then data(i, 28) = CLng(Format(data(i, 3), "ww"))
Next
tbl.Value = data 'return the data
End Sub