VBA Macro is excruciatingly slow - excel

Question

Currently i have a perfectly functioning VBA Macro. Does everything it is required to. However, i do need some advice and help on speeding this macro up as it takes a LONG time to get things done. This macro takes aroung 5 minutes to sort through around 4k-5k populated rows, which then it hides some of the rows.
How this macro works is that it will sort through Column A, sorting through the names and comparing it to a list in Sheet1, where if the name matches the list in sheet1, it will proceed to hide the row.
Thanks in advance.
Sub FilterNameDuplicate()
Application.ScreenUpdating = False
Dim iListCount As Integer
Dim iCtr As Integer
Dim a As Long
Dim b As Long
Dim c As Long
Dim D As Long
a = Worksheets("Default").Cells(Rows.Count, "G").End(xlUp).Row
For c = 1 To a
b = Worksheets("Sheet1").Cells(Rows.Count, "A").End(xlUp).Row
For D = 1 To b
If StrComp(Worksheets("Sheet1").Cells(D, "A"), (Worksheets("Default").Cells(c, "G")), vbTextCompare) = 0 Then
Worksheets("Default").Rows(c).EntireRow.Hidden = True
End If
Next
Next
Application.ScreenUpdating = True
MsgBox "Done"
End Sub

Answer 1

All of your accesses to the worksheet really slows things down.
Much faster to use VBA arrays.
You can eliminate some of the looping by using the Range.Find method to determine if there are duplicates of the names on Default in Sheet1.
We collect the non-duplicated names (in a Collection) and then create an array to use as the argument for the Range.Filter method (which will effectively hide the entire row).
Accordingly:
Code edited to run faster using Match function
Option Explicit
Sub FilterNameDuplicate()
Dim ws1 As Worksheet, wsD As Worksheet
Dim v1 As Variant, vD As Variant, r1 As Range, rD As Range
Dim col As Collection
Dim R As Range, I As Long, arrNames() As String
With ThisWorkbook
Set ws1 = .Worksheets("Sheet1")
Set wsD = .Worksheets("Default")
End With
With ws1
Set r1 = Range(.Cells(1, 1), .Cells(.Rows.Count, 1).End(xlUp))
v1 = r1
End With
With wsD
Set rD = Range(.Cells(1, 7), .Cells(.Rows.Count, 7).End(xlUp))
vD = rD
End With
'collect names on Default that are not on Sheet1
Set col = New Collection
With Application
For I = 2 To UBound(vD, 1)
If .WorksheetFunction.IsError(.Match(vD(I, 1), v1, 0)) Then col.Add vD(I, 1)
Next I
End With
'Filter to include those names
Application.ScreenUpdating = False
If wsD.FilterMode Then wsD.ShowAllData
ReDim arrNames(1 To col.Count)
For I = 1 To col.Count
arrNames(I) = col(I)
Next I
rD.AutoFilter field:=1, Criteria1:=arrNames, Operator:=xlFilterValues
End Sub

Answer 2

The main slow down is do to nested looping. Using a Collection or Dictionary for quicker lookups will speed up your code 100 times.
Sub FilterNameDuplicate()
Application.ScreenUpdating = False
Application.Calculation = xlCalculationManual
Rem Unhide all the rows
Worksheets("Default").UsedRange.EntireRow.Hidden = False
Dim Keys As Collection
Set Keys = GKeys
Dim Key As String
Dim Target As Range
With Worksheets("Default")
Set Target = Intersect(.UsedRange, .Columns("G"))
End With
If Target Is Nothing Then
MsgBox "Invalid Range"
Exit Sub
End If
Dim Cell As Range
For Each Cell In Target
Key = UCase(Cell.Value)
On Error Resume Next
Key = Keys(Key)
Cell.EntireRow.Hidden = Err.Number <> 0
On Error GoTo 0
Next
Rem We no longer need to turn ScreenUpdating back on
Application.Calculation = xlCalculationAutomatic
MsgBox "Done"
End Sub
Function GKeys() As Collection
Set GKeys = New Collection
Dim Key As String
Dim Data As Variant
Data = Worksheets("Sheet1").Range("A1").CurrentRegion.Columns(1).Value
Dim r As Long
For r = 1 To UBound(Data)
Key = UCase(Data(r, 1))
On Error Resume Next
GKeys.Add Key:=Key, Item:=""
On Error GoTo 0
Next
End Function

Answer 3

Trying adding in this, it speeds up by turning off screen updating, events, animations etc, this should speed it up a bit!
At the start of your code add in this sub
Call TurnOffCode
At the end of your code add in this sub
Call TurnOnCode
This is what they should both look like
Sub TurnOffCode() 'Used to turn off settings to make workbook run faster
Application.Calculation = xlCalculationManual 'Set calculations to manual
Application.ScreenUpdating = False 'Turns off screen updating
Application.EnableEvents = False 'Turns off events
Application.EnableAnimations = False 'Turns off animations
Application.DisplayStatusBar = False 'Turns off display status bar
Application.PrintCommunication = False 'Turns off print communications
End Sub
Sub TurnOnCode() 'Used to turn settings back on to normal
Application.Calculation = xlCalculationAutomatic 'Set calculations to automatic
Application.ScreenUpdating = True 'Turns on screen updating
Application.EnableEvents = True 'Turns on events
Application.EnableAnimations = True 'Turns on animations
Application.DisplayStatusBar = True 'Turns on display status bar
Application.PrintCommunication = True 'Turns on print communications
End Sub