Excel VBA correct/efficient formula population - excel

Question

Good Afternoon,
I have been developing solutions in VBA for going on 6 years now. A lot of what I have learned along the way has been sourced from SO in that time, so finally I get a chance to say THANK YOU!
Today I have come to the conclusion that I need to post a question that has been bothering me for years. So - one of the things I do most often in VBA for Excel is to populate defined ranges with results from formulas applied to the range in question. Until now I have used the below method to accomplish this:
Sub CalculateField()
Application.ScreenUpdating = False
Application.DisplayAlerts = False
'''''''''''''''''''''''''''''''''
Dim RecordStop As Long
Set MyRange = ActiveSheet.Range("A:A")
RecordStop = Application.WorksheetFunction.CountA(MyRange)
'Apply Formula
Range("M2:M" & RecordStop).FormulaR1C1 = "=IF(RC[-7]=1,IF(ISERROR(VLOOKUP(CONCATENATE(RC[-2],""|"",1),R1C12:R[-1]C[-1],1,FA LSE)),0,1),0)"
'Drop Formula, keep values
Range("M2:M" & RecordStop).Value = Range("M2:M" & RecordStop).Value
''''''''''''''''''''''''''''''''''
Application.ScreenUpdating = True
Application.DisplayAlerts = True
End Sub
What I have found is that, although this method works, with larger files/more complex formula the hit I take in performance is HUGE! Now, I know that there must be a more efficient way to derive the results of the formula and inject them directly into the sheet where one wants the results to come back to as values. In the above method I first calculate the results then overwrite the "Formulas" with the "values"(results). I am currently working on a file that will need 21 calculated fields and average between 100k - 400k records.
I fear the time has come for me to learn a better way, the proper more professional way to do this. I have searched here and via the mighty google for examples on how to do this. I have found posts on SO describing what I think is part of the solution, but have had difficulty finding a specific simple example I can follow to implement. I think the correct method involves one or all of the following:
Arrays
Dictionaries
Collections
... I hope you guys can point me in the right direction. This, once solved, I feel will greatly up my game in VBA development. I have been hesitant to delve into this as I am self educated and never really thought I would get this far as it is not my primary role, but would love to get past this now so I would greatly appreciate your assistance.
BTW; I am pretty good at self learning, so if by chance there is already a post that can get me there just point the way. Again, in searching I could not find what I was looking for so I apologize if that was a result of not knowing how to (words to describe) look for the answer.

Answer 1

I might start with this before tinkering a bunch.
If you don't get a performance boost, I'd then consider pulling your source data into Arrays, modify them in code, then write your results in a one line of code write back to your cells.
Here's a great link for working the Array route: VBA Arrays And Worksheet Ranges
Dim PrevCalc As XlCalculation
With Application
PrevCalc = .Calculation
.Calculation = xlCalculationManual
.Cursor = xlWait
.Calculate
.EnableEvents = False
.ScreenUpdating = False
End With
Dim RecordStop As Long
Set MyRange = ActiveSheet.Range("A:A")
RecordStop = Application.WorksheetFunction.CountA(MyRange)
'Apply Formula
With Range("M2:M" & RecordStop)
.FormulaR1C1 = "=IF(RC[-7]=1,IF(ISERROR(VLOOKUP(CONCATENATE(RC[-2],""|"",1),R1C12:R[-1]C[-1],1,FA LSE)),0,1),0)"
'Calc only the target
.Calculate
'Drop Formula, keep values
.Value = .Value
End With 'Range("M2:M" & RecordStop)
With Application
.Cursor = xlDefault
.Calculate
.Calculation = PrevCalc
'.ScreenUpdating = True 'Not Needed...
.EnableEvents = True
End With