Slice array to use index on larger than 65000 - arrays

Question

I use the code hereunder to calculate max values as described in this post (vba max value of group of values). The code works great but once I have more than 65k lines I get a data type mismatch when trying to pase the array:
sht.Range(Cells(1, lColumn), Cells(last.Row, lColumn)).Value = Application.Index(groupsArray, , lColumn)
Could somebody help me to slice the array in chunks. I have tried to get it working myself but without any luck.
Sub FillGroupsMax()
Dim lColumn As Long
Dim sht As Worksheet
Dim groupsArray As Variant 'array with all group infomation
Dim groupsSeen As Variant 'array with group infomation already seen
Application.ScreenUpdating = False 'stop screen updating makes vba perform better
Set sht = ThisWorkbook.Worksheets("import")
Set last = sht.Range("A:A").Find("*", Cells(1, 1), searchdirection:=xlPrevious) 'last cell with value in column A
lColumn = sht.Cells(1, Columns.Count).End(xlToLeft).Column
groupsArray = sht.Range(Cells(1, 1), Cells(last.Row, lColumn))
'collect all the information on the Sheet into an array
'Improves performance by not visiting the sheet
For dRow = 2 To last.Row 'for each of the rows skipping header
'check if group as already been seen
If inArrayValue(Cells(dRow, 1).Value, groupsSeen) > 0 Then
'if it has been seen/calculated attribute value
'Cells(dRow, 4).Value = inArrayValue(Cells(dRow, 1).Value, groupsSeen)
groupsArray(dRow, lColumn) = inArrayValue(Cells(dRow, 1).Value, groupsSeen)
Else
'if it hasn't been seen then find max
'Cells(dRow, 4).Value = getMax(Cells(dRow, 1).Value, groupsArray)
groupsArray(dRow, lColumn) = getMax(Cells(dRow, 1).Value, groupsArray, lColumn)
'array construction from empty
If IsEmpty(groupsSeen) Then
ReDim groupsSeen(0)
'groupsSeen(0) = Array(Cells(dRow, 1).Value, Cells(dRow, 4).Value)
groupsSeen(0) = Array(groupsArray(dRow, 1), groupsArray(dRow, lColumn))
'attribute value to array
Else
ReDim Preserve groupsSeen(0 To UBound(groupsSeen) + 1)
groupsSeen(UBound(groupsSeen)) = Array(groupsArray(dRow, 1), groupsArray(dRow, lColumn))
End If
End If
Next
sht.Range(Cells(1, lColumn), Cells(last.Row, lColumn)).Value = Application.Index(groupsArray, , lColumn)
'reactivate Screen updating
Application.ScreenUpdating = True
End Sub
Function getMax(group As String, groupsArray As Variant, lColumn As Long) As Double
'for each in array
For n = 1 To UBound(groupsArray)
'if its the same group the Max we seen so far the record
If groupsArray(n, 1) = group And groupsArray(n, lColumn - 1) > maxSoFar Then
maxSoFar = groupsArray(n, lColumn - 1)
End If
Next
'set function value
getMax = maxSoFar
End Function
Function inArrayValue(group As String, groupsSeen As Variant) As Double
'set function value
inArrayValue = 0
'if array is empty then exit
If IsEmpty(groupsSeen) Then Exit Function
'for each in array
For n = 0 To UBound(groupsSeen)
'if we find the group
If groupsSeen(n)(0) = group Then
'set function value to the Max value already seen
inArrayValue = groupsSeen(n)(1)
'exit function earlier
Exit Function
End If
Next
End Function

Answer 1

You can write a helper function to use instead of Application.Index
Bonus - it will be much faster than using Index (>5x)
Sub Tester()
Dim arr, arrCol
arr = Range("A2:J80000").Value
arrCol = GetColumn(arr, 5) '<< get the fifth column
Range("L2").Resize(UBound(arrCol, 1), 1).Value = arrCol
End Sub
'extract a single column from a 1-based 2-D array
Function GetColumn(arr, colNumber)
Dim arrRet, i As Long
ReDim arrRet(1 To UBound(arr, 1), 1 To 1)
For i = 1 To UBound(arr, 1)
arrRet(i, 1) = arr(i, colNumber)
Next i
GetColumn = arrRet
End Function
EDIT - since QHarr asked about timing here's a basic example
Sub Tester()
Dim arr, arrCol, t, i as long
arr = Range("A2:J80000").Value
t = Timer
For i = 1 to 100
arrCol = GetColumn(arr, 5) '<< get the fifth column
Next i
Debug.print Timer - t '<<# of seconds for execution
End Sub

Answer 2

Below, whilst not as tidy as could be, is a way to process an array in chunks and Index to access a column and write out to the sheet.
I populated two columns (A:B) with data. Both had 132,000 rows, populated incrementally, with values from 1 to 132,000 in each column for my test run.
You can fiddle with cutOff to get the chunk size just below the point where the fail happens.
The code below is simply to demonstrate the principle of looping in batches, upto the set cutoff in each batch, until all rows have been processed.
Option Explicit
Public Sub WriteArrayToSheet()
Dim wb As Workbook
Dim ws As Worksheet
Set wb = ThisWorkbook
Set sht = wb.Worksheets("Sheet1") 'change as appropriate
Dim myArr() 'dynamic array
myArr = sht.Range("A1").CurrentRegion.Value 'you may want a more robust method
Dim cutOff As Long 'the max value - what ever it is before error occurs
cutOff = 1000
Dim totalRows As Long 'total rows in array read in from sheet
totalRows = UBound(myArr, 1)
Dim totalArraysNeeded As Long
'Determine how many lots of cutOff chunks there are in the total number of array rows
totalArraysNeeded = Application.WorksheetFunction.Ceiling(totalRows / cutOff, 1)
Dim rotations As Long 'number of times to loop original array to handle all rows
Dim rowCountTotal As Long
Dim rowCount As Long
Dim tempArr() 'this will hold the chunk of the original array
Dim rowCounter As Long
Dim lastRow As Long
Dim nextRow As Long
Dim i As Long
Dim j As Long
Dim numRows As Long
rotations = 1
Do While rotations < totalArraysNeeded
If rotations < totalArraysNeeded - 1 Then
ReDim tempArr(1 To cutOff, 1 To UBound(myArr, 2)) 'size chunk array
numRows = cutOff
Else
numRows = totalRows - rowCountTotal
ReDim tempArr(1 To numRows, 1 To UBound(myArr, 2)) 'size chunk array
End If
For i = 1 To numRows
rowCount = 1 'rows in this chunk looped
rowCountTotal = rowCountTotal + 1 'rows in original array looped
For j = LBound(myArr, 2) To UBound(myArr, 2)
tempArr(i, j) = myArr(rowCountTotal, j)
Next j
rowCount = rowCount + 1
Next i
With sht
lastRow = .Cells(.Rows.Count, "E").End(xlUp).Row 'Column where I am writing the sliced column out to
End With
If lastRow = 1 Then
nextRow = 1
Else
nextRow = lastRow + 1
End If
sht.Range("E" & nextRow).Resize(UBound(tempArr, 1), 1) = Application.Index(tempArr, , 1) 'write out to sheet
rotations = rotations + 1
Loop
End Sub

Answer 3

As #Tim suggested, the best way to slice a large array is use a loop to copy the column.
Though in your case, most of the processing time is spent on computing the maximum since your code is using a nested loop.
If you want to reduce significantly the processing time, then use a dictionary:
Sub Usage
GetMaxByGroupTo _
sourceGroups := ThisWorkbook.Range("Sheet1!A2:A100"), _
sourceValues := ThisWorkbook.Range("Sheet1!B2:B100"), _
target := ThisWorkbook.Range("Sheet1!C2")
End Sub
Sub GetMaxByGroupTo(sourceGroups As Range, sourceValues As Range, target As Range)
Dim dict As Object, groups(), values(), r As Long, max
Set dict = CreateObject("Scripting.Dictionary")
groups = sourceGroups.Value2
values = sourceValues.Value2
' store the maximum value of each group in a dictionary for an efficient lookup '
For r = Lbound(groups) to Ubound(groups)
max = dict(groups(r, 1))
If VarType(max) And values(r, 1) <= max Then Else dict(groups(r, 1)) = values(r, 1)
Next
' build and copy the result array to the sheet '
For r = Lbound(groups) to Ubound(groups)
values(r, 1) = dict(groups(r, 1))
Next
target.Resize(Ubound(groups), 1).Value2 = values
End Sub