Speed up For Loop by using an Array - arrays

Question

I'm looking to speed up a For Loop (as per code below) by incorporating the use of an Array.
Would really appreciate some advice on how to do this:
Sub DetectedCheck()
'counts rows in sheet 1 and 2.
With Sheets(1)
reconrows = .Range("a" & .Rows.Count).End(xlUp).Row
End With
'Checks that the new data has both an assigned and detected role and adds "No Issue" to column Q if valid.
For i = 2 To reconrows
If ActiveWorkbook.Sheets(1).Range("J" & i).Value <> "Not Found" And ActiveWorkbook.Sheets(1).Range("K" & i).Value <> "" Then
ActiveWorkbook.Sheets(1).Range("S" & i).Value = "No Issue"
End If
Next i
End Sub

Answer 1

Please, try the next way:
Sub DetectedCheck()
Dim sh As Worksheet, reconRows As Long, arrJK, arrS, i As Long
Set sh = Sheets(1)
reconRows = sh.Range("a" & sh.rows.count).End(xlUp).row
arrJK = sh.Range("J2:K" & reconRows).value
arrS = sh.Range("S2:S" & reconRows).value
'Checks that the new data has both an assigned and detected role and adds "No Issue" to column Q if valid.
For i = 1 To UBound(arrJK)
If arrJK(i, 1) <> "Not Found" And arrJK(i, 2) <> "" Then
arrS(i, 1) = "No Issue"
End If
Next i
sh.Range("S2").Resize(UBound(arrS), 1).value = arrS
End Sub
But in the code comment you mention "No Issue" to column Q" and in your code you use S:S column. Please, adapt if the return must be done in Q:Q.

Answer 2

Want to test this method and see the speed of looping with arrays compared to rows?
Dim timmy, i As Long, rc As Long, arr1, arr2, arr3
timmy = Timer
With Sheets(1)
rc = .Range("A" & Rows.Count).End(xlUp).Row
arr1 = .Range("J2:J" & rc).Value
arr2 = .Range("K2:K" & rc).Value
ReDim arr3(1 To UBound(arr1), 1 To 1)
For i = 1 To UBound(arr1, 1)
If arr1(i, 1) = "Not Found" And IsEmpty(arr2(i, 1)) Then
arr3(i, 1) = ""
Else
arr3(i, 1) = "No Issue"
End If
Next i
.Range("S2:S" & rc).Value = arr3
End With
Debug.Print "Loopy", Timer - timmy

Answer 3

Loop Through Arrays Instead of Ranges
To speed up a loop, you can turn off the three most common 'speed-related' application settings: ScreenUpdating, Calculation, and EnableEvents. Often it doesn't help much.
The trick is to access the worksheet as few times as possible i.e. to write the values of the ranges to arrays (you could think of these 2D one-based arrays as ranges (in this case column ranges) in memory, starting in row 1, since they are handled similarly), loop over the arrays and write the results to another (resulting) array and write the values from the latter array to the resulting range.
The first code, the array code, took roughly 0.3 seconds for 100.000 rows of simple sample data (created with the PopulateRandomData procedure) resulting in about 25.000 No Issue cells.
For the same data, the second code, the range code, took roughly 2.5 seconds when the resulting (destination) column range was cleared previously. It took about 5 seconds if each cell was cleared in the loop (a mistake). It took 40 seconds if vbNullString or Empty were written in the loop (a huge mistake).
So the array code was roughly 8 times faster but depending on your data and how the code was previously written, the array code could be many more (tens or even hundreds of) times faster.
Note that the running times will be different for your data so your feedback is appreciated.
Check out these Excel Macro Mastery videos to quickly learn about arrays and their use to speed up code.
Option Explicit
Sub DetectedCheckArray()
' Constants
Const wsID As Variant = 1 ' safer is to use the (tab) name, e.g. "Sheet1"
Const fRow As Long = 2
Const lrCol As String = "A" ' Last Row Column
Const c1Col As String = "J" ' 1st Criteria Column
Const c2Col As String = "K" ' 2nd Criteria Column
Const NotCrit1 As String = "Not Found" ' 1st Criteria
Const NotCrit2 As String = "" ' 2nd Criteria
Const dCol As String = "S" ' Destination Column
Const dString As String = "No Issue"
' If you use constants at the beginning of the code,
' you can easily change their values in one place without
' searching in the code.
' Reference the workbook ('wb').
Dim wb As Workbook: Set wb = ThisWorkbook ' workbook containing this code
' Reference the worksheet ('ws') (in the workbook).
Dim ws As Worksheet: Set ws = wb.Worksheets(wsID) '
' Calculate the last row ('lRow'),
' the row of the last non-empty cell in the column.
Dim lRow As Long: lRow = ws.Cells(ws.Rows.Count, lrCol).End(xlUp).Row
' Calculate the number of rows ('rCount').
Dim rCount As Long: rCount = lRow - fRow + 1
' Note that all ranges and arrays have this number of rows ('rCount').
' Validate the number of rows.
If rCount < 1 Then
MsgBox "No data in column range.", vbCritical
Exit Sub
End If
' Reference the last row (one-column) range ('lrrg') to be used
' to easily reference the remaining ranges.
Dim lrrg As Range
' This may be more understandable (commonly used),...
Set lrrg = ws.Range(ws.Cells(fRow, lrCol), ws.Cells(lRow, lrCol))
' ... but I prefer:
'Set lrrg = ws.Cells(fRow, lrCol).Resize(rCount)
' Reference the criteria (one-column) ranges ('crg1' and 'crg2').
Dim crg1 As Range: Set crg1 = lrrg.EntireRow.Columns(c1Col)
Dim crg2 As Range: Set crg2 = lrrg.EntireRow.Columns(c2Col)
' If you have a reference to a one-column range ('lrrg') and you want
' to reference the same range in another worksheet column ('c1Col, c2Col'),
' use '.EntireRow' to easily do it, to not complicate with '.Offset'.
' The code so far runs in split seconds.
' The following is the improvement.
' Start measuring the time passed.
Dim dt As Double: dt = Timer
' Write the values from the criteria ranges
' to 2D one-based one-column arrays ('cData1' and 'cData2').
Dim cData1() As Variant
Dim cData2() As Variant
If rCount = 1 Then ' one cell
ReDim cData1(1 To 1, 1 To 1): cData1(1, 1) = crg1.Value
ReDim cData2(1 To 1, 1 To 1): cData1(1, 1) = crg2.Value
Else ' multiple cells
cData1 = crg1.Value
cData2 = crg2.Value
End If
' Define the destination string array ('dsData').
Dim dsData() As String: ReDim dsData(1 To rCount, 1 To 1)
Dim r As Long
' Loop through the rows ('r') of the arrays and for each row
' check the values of the criteria arrays against the (not) criterias.
' If all (both) conditions are met, write the destination string ('dString')
' to the current row of the destination string array.
For r = 1 To rCount
If StrComp(CStr(cData1(r, 1)), NotCrit1, vbTextCompare) <> 0 Then
If StrComp(CStr(cData2(r, 1)), NotCrit2, vbTextCompare) <> 0 Then
dsData(r, 1) = dString
End If
End If
Next r
' Reference the destination (one-column) range ('drg').
Dim drg As Range: Set drg = lrrg.EntireRow.Columns(dCol)
' Write the values from the destination string array
' to the destination range.
drg.Value = dsData
' Inform.
MsgBox "Finished in " & Timer - dt & " seconds.", vbInformation
End Sub
Sub DetectedCheckRange()
' Constants
Const wsID As Variant = 1 ' safer is to use the (tab) name, e.g. "Sheet1"
Const fRow As Long = 2
Const lrCol As String = "A" ' Last Row Column
Const c1Col As String = "J" ' 1st Criteria Column
Const c2Col As String = "K" ' 2nd Criteria Column
Const NotCrit1 As String = "Not Found" ' 1st Criteria
Const NotCrit2 As String = "" ' 2nd Criteria
Const dCol As String = "S" ' Destination Column
Const dString As String = "No Issue"
' If you use constants at the beginning of the code,
' you can easily change their values in one place without
' searching in the code.
' Reference the workbook ('wb').
Dim wb As Workbook: Set wb = ThisWorkbook ' workbook containing this code
' Reference the worksheet ('ws') (in the workbook).
Dim ws As Worksheet: Set ws = wb.Worksheets(wsID) '
' Calculate the last row ('lRow'),
' the row of the last non-empty cell in the column.
Dim lRow As Long: lRow = ws.Cells(ws.Rows.Count, lrCol).End(xlUp).Row
' Calculate the number of rows ('rCount').
Dim rCount As Long: rCount = lRow - fRow + 1
' Note that all ranges and arrays have this number of rows ('rCount').
' Validate the number of rows.
If rCount < 1 Then
MsgBox "No data in column range.", vbCritical
Exit Sub
End If
' Reference the last row (one-column) range ('lrrg') to be used
' to easily reference the remaining ranges.
Dim lrrg As Range
' This may be more understandable (commonly used),...
Set lrrg = ws.Range(ws.Cells(fRow, lrCol), ws.Cells(lRow, lrCol))
' ... but I prefer:
'Set lrrg = ws.Cells(fRow, lrCol).Resize(rCount)
' Reference the criteria (one-column) ranges ('crg1' and 'crg2').
Dim crg1 As Range: Set crg1 = lrrg.EntireRow.Columns(c1Col)
Dim crg2 As Range: Set crg2 = lrrg.EntireRow.Columns(c2Col)
' If you have a reference to a one-column range ('lrrg') and you want
' to reference the same range in another worksheet column ('c1Col, c2Col'),
' use '.EntireRow' to easily do it, to not complicate with '.Offset'.
' Reference the destination (one-column) range ('drg').
Dim drg As Range: Set drg = lrrg.EntireRow.Columns(dCol)
' The code so far runs in split seconds.
' The following loop is what is slowing down the code.
' Start measuring the time passed.
Dim dt As Double: dt = Timer
' Turn off application settings to speed up.
Application.ScreenUpdating = False
Application.Calculation = xlCalculationManual
Application.EnableEvents = False
drg.ClearContents ' or drg.clear (2.5 seconds)
Dim r As Long
' Loop through the rows ('r') of the column ranges and for each row
' check the values of the criteria ranges against the (not) criterias.
' If all (both) conditions are met, write the destination string ('dString')
' to the current row of the destination column.
For r = 1 To rCount
If StrComp(CStr(crg1.Cells(r).Value), NotCrit1, vbTextCompare) <> 0 Then
If StrComp(CStr(crg2.Cells(r).Value), NotCrit2, vbTextCompare) _
<> 0 Then
drg.Cells(r).Value = dString
Else ' The following line may or may not be necessary.
' Mistake, clear the complete range before (5 seconds).
'drg.Cells(r).Clear ' Contents ' or drg.Cells(r).Clear
' Huge mistake, use clear instead (40 seconds).
'drg.Cells(r).Value = Empty
'drg.Cells(r).Value = vbNullString
End If
End If
Next r
' Turn on application settings.
Application.EnableEvents = True
Application.Calculation = xlCalculationAutomatic
Application.ScreenUpdating = True
' Inform.
MsgBox "Finished in " & Timer - dt & " seconds.", vbInformation
End Sub
Sub PopulateRandomData()
Const rCount As Long = 100000
With ThisWorkbook.Worksheets(1)
.UsedRange.Clear
.Range("C:H,M:Q").EntireColumn.Hidden = True
With .Range("A2").Resize(rCount)
.Cells(1).Offset(-1).Value = "LrCol"
.Value = .Worksheet.Evaluate("ROW(1:" & CStr(rCount + 1) & ")")
.EntireColumn.AutoFit
End With
With .Range("J2").Resize(rCount)
.Cells(1).Offset(-1).Value = "Criteria1"
.Formula = "=CHOOSE(RANDBETWEEN(1,2),""Found"",""Not Found"")"
.Value = .Value
.EntireColumn.AutoFit
End With
With .Range("K2").Resize(rCount)
.Cells(1).Offset(-1).Value = "Criteria2"
.Formula = "=CHOOSE(RANDBETWEEN(1,2),""String"","""")"
.Value = .Value
.EntireColumn.AutoFit
End With
With .Range("S1")
.Value = "Result No Issue"
.EntireColumn.AutoFit
End With
End With
End Sub