excel vba - efficiently loop 2d array

Question

I'm hopelessly trying to find a better way of filling a range contents. This way produces the correct results but is very slow. Can anyone point me in the correct direction in terms of how to fill a 2d array or otherwise to speed up the algorithm? I would love a code snippet someone has had success with or even just links that show a cleaner method.

here is my OLD code:
----------------
    f = 1
    maxcol = 'func call to get last non blank col ref .ie could return T, R, H.etc

    For f = 1 To UBound(filenames)
        Set aDoc = LoadXmlDoc(filenames(f))
        For Each c In Worksheets("Results").Range("A1:" & maxcol & "1")
                                        c.Offset(f, 0).Value = aNode.Text
                    Next c
        Worksheets("Results").Range(maxcol & "1").Offset(f, 0).Value = filenames(f)
    Next f


UPDATED CODE:
----------

Dim aDoc As DOMDocument
Dim aNode As IXMLDOMNode
Dim numOfXpaths As Integer
Dim filenames As Variant
Dim f As Integer
Dim maxcol As String
Dim rngStart As Range
Dim nColIndex As Long
Dim lngCalc As Long
'Dim numOfFiles As Integer
Dim aXpaths As Variant
        numOfFiles = UBound(filenames)
    colToRow aXpaths, numOfXpaths
    maxcol = Number2Char(numOfXpaths)
        ReDim aValues(1 To numOfFiles, 1 To numOfXpaths + 1) As Variant
        For f = 1 To numOfFiles
            Set aDoc = LoadXmlDoc(filenames(f))
            For nColIndex = 1 To numOfXpaths
                    If aDoc.parseError Then
                        aValues(f, nColIndex) = "XML parse error:" 
                    Else
                      Set aNode = aDoc.selectSingleNode(aXpaths(nColIndex))
                      aValues(f, nColIndex) = aNode.Text
                    End If
            Next nColIndex
            aValues(f, numOfXpaths + 1) = filenames(f)
        Next f
        Worksheets("Results").Range("A1").Offset(1, 0).Resize(numOfFiles, numOfXpaths + 1).Value = aValues


    Function colToRow(ByRef aXpaths As Variant, ByRef numOfXpaths As Integer)
    Dim xpathcount As Integer
    Dim c As Integer
    'Dim aXpaths As Variant
    xpathcount = Worksheets("Xpaths").Cells(Rows.Count, "A").End(xlUp).Row - 1
    ReDim aXpaths(1 To xpathcount + 1) As Variant
    For c = 0 To xpathcount
        Worksheets("Results").Range("A1").Offset(0, c) = Worksheets("Xpaths").Range("A1").Offset(c, 0)
        Worksheets("Results").Range("A1").Offset(0, c).Columns.AutoFit
        aXpaths(c + 1) = Worksheets("Xpaths").Range("A1").Offset(c, 0)
    Next c
    Worksheets("Results").Range("A1").Offset(0, xpathcount + 1) = "Filename"
    'colToRow = xpathcount + 1
    numOfXpaths = xpathcount + 1
    End Function

Function Number2Char(ByVal c) As String
Number2Char = Split(Cells(1, c).Address, "$")(1)
End Function

Answer 1

You might want to look at my code in "Using Variant Arrays in Excel VBA for Large Scale Data Manipulation", http://www.experts-exchange.com/A_2684.html (further detail provided in the hyperlink)

Note that as I don't have your data above to work with the article provides a sample solution (in this case efficiently deleting leading zeroes) to meet you filling a range from a 2d array requirement.

Key points to note

1. The code handles non contigious ranges by use of Areas
2. When using variant arrays alwasy test that the range setting the array size is bigger than 1 cell - if not you cant use a variant
3. The code readas from a range, runs a manipulation, then dumps back to the same range
4. Using Value2 is slightly moe efficient than Value

Here is the code:

'Press Alt + F11 to open the Visual Basic Editor (VBE)
'From the Menu, choose Insert-Module.
'Paste the code into the right-hand code window.
'Press Alt + F11 to close the VBE
'In Xl2003 Goto Tools … Macro … Macros and double-click KillLeadingZeros

Sub KillLeadingZeros()
    Dim rng1 As Range
    Dim rngArea As Range
    Dim lngRow As Long
    Dim lngCol As Long
    Dim lngCalc As Long
    Dim objReg As Object
    Dim X()


    On Error Resume Next
    Set rng1 = Application.InputBox("Select range for the replacement of leading zeros", "User select", Selection.Address, , , , , 8)
    If rng1 Is Nothing Then Exit Sub
    On Error GoTo 0

    'See Patrick Matthews excellent article on using Regular Expressions with VBA
    Set objReg = CreateObject("vbscript.regexp")
    objReg.Pattern = "^0+"

    'Speed up the code by turning off screenupdating and setting calculation to manual
    'Disable any code events that may occur when writing to cells
    With Application
        lngCalc = .Calculation
        .ScreenUpdating = False
        .Calculation = xlCalculationManual
        .EnableEvents = False
    End With

    'Test each area in the user selected range

    'Non contiguous range areas are common when using SpecialCells to define specific cell types to work on
    For Each rngArea In rng1.Areas
        'The most common outcome is used for the True outcome to optimise code speed
        If rngArea.Cells.Count > 1 Then
           'If there is more than once cell then set the variant array to the dimensions of the range area
           'Using Value2 provides a useful speed improvement over Value. On my testing it was 2% on blank cells, up to 10% on non-blanks    
            X = rngArea.Value2
            For lngRow = 1 To rngArea.Rows.Count
                For lngCol = 1 To rngArea.Columns.Count
                    'replace the leading zeroes
                    X(lngRow, lngCol) = objReg.Replace(X(lngRow, lngCol), vbNullString)
                Next lngCol
            Next lngRow
            'Dump the updated array sans leading zeroes back over the initial range
            rngArea.Value2 = X
        Else
            'caters for a single cell range area. No variant array required
            rngArea.Value = objReg.Replace(rngArea.Value, vbNullString)
        End If
    Next rngArea

    'cleanup the Application settings
    With Application
        .ScreenUpdating = True
        .Calculation = lngCalc
        .EnableEvents = True
    End With

    Set objReg = Nothing
    End Sub

Answer 2

To do this efficiently you should generate a 2-dimensional data with the data you want to write, then write it all in one go.

Something like the following. I prefer 0-based arrays for compatibility with other languages whereas you seem to be using a 1-based array (1 to UBound(filenames). So there may be off-by-one errors in the following untested code:

f = 1
maxcol = 'func call to get last non blank col ref .ie could return T, R, H.etc

' 2D array to hold results    
' 0-based indexing: UBound(filenames) rows and maxcol columns
Dim aValues(0 to UBound(filenames)-1, 0 To maxcol-1) As Variant
Dim rngStart As Range
Dim nColIndex As Long

For f = 1 To UBound(filenames)
    Set aDoc = LoadXmlDoc(filenames(f))

    aValues(f-1, 0) = filenames(f)

    For nColIndex = 1 To maxCol-1
        aValues(f-1, nColIndex) = aNode.Text
    Next nColIndex

Next f

' Copy the 2D array in one go
Worksheets("Results").Offset(1,0).Resize(UBound(filenames),maxCol).Value = aValues

Answer 3

As you're getting you results from XML, have you looked into using XML Maps to display the information - might not be suitable for your situation, but worth a try.

This link below shows some stuff about using XML maps in Excel.

The syntax of the line to load an XML string into a define map is similar to this:

ActiveWorkbook.XmlMaps("MyMap").ImportXml(MyXMLDoc,True)