How do I slice an array in Excel VBA?

Two things, VBA doesn't support array slicing so whatever you use, you'll have to roll your own. But since this is just for Excel, you can use the build in worksheet function index for array slicing.

Sub Test()
    'All example return a 1 based 2D array.
    Dim myArr As Variant 'This var must be generic to work.
    'Get whole range:
    myArr = ActiveSheet.UsedRange
    'Get just column 1:
    myArr = WorksheetFunction.Index(ActiveSheet.UsedRange, 0, 1)
    'Get just row 5
    myArr = WorksheetFunction.Index(ActiveSheet.UsedRange, 5, 0)
End Sub

Application.WorksheetFunction.Index(array, row, column)

If you specify a zero value for row or column, then you'll get the entire column or row that is specified.

Example:

Application.WorksheetFunction.Index(array, 0, 3)

This will give you the entire 3rd column.

If you specify both row and column as non-zero, then you'll get only the specific element. There is no easy way to get a smaller slice than a complete row or column.

Limitation: There is a limit to the array size that WorksheetFunction.Index can handle if you're using a newer version of Excel. If array has more than 65,536 rows or 65,536 columns, then it throws a "Type mismatch" error. If this is an issue for you, then see this more complicated answer which is not subject to the same limitation.

Here's the function I wrote to do all my 1D and 2D slicing:

Public Function GetArraySlice2D(Sarray As Variant, Stype As String, Sindex As Integer, Sstart As Integer, Sfinish As Integer) As Variant

' this function returns a slice of an array, Stype is either row or column
' Sstart is beginning of slice, Sfinish is end of slice (Sfinish = 0 means entire
' row or column is taken), Sindex is the row or column to be sliced
' (NOTE: 1 is always the first row or first column)
' an Sindex value of 0 means that the array is one dimensional 3/20/09 ljr

Dim vtemp() As Variant
Dim i As Integer

On Err GoTo ErrHandler

Select Case Sindex
    Case 0
        If Sfinish - Sstart = UBound(Sarray) - LBound(Sarray) Then
            vtemp = Sarray
        Else
            ReDim vtemp(1 To Sfinish - Sstart + 1)
            For i = 1 To Sfinish - Sstart + 1
                vtemp(i) = Sarray(i + Sstart - 1)
            Next i
        End If
    Case Else
        Select Case Stype
            Case "row"
                If Sfinish = 0 Or (Sstart = LBound(Sarray, 2) And Sfinish = UBound(Sarray, 2)) Then
                    vtemp = Application.WorksheetFunction.Index(Sarray, Sindex, 0)
                Else
                    ReDim vtemp(1 To Sfinish - Sstart + 1)
                    For i = 1 To Sfinish - Sstart + 1
                        vtemp(i) = Sarray(Sindex, i + Sstart - 1)
                    Next i
                End If
            Case "column"
                If Sfinish = 0 Or (Sstart = LBound(Sarray, 1) And Sfinish = UBound(Sarray, 1)) Then
                    vtemp = Application.WorksheetFunction.Index(Sarray, 0, Sindex)
                Else
                    ReDim vtemp(1 To Sfinish - Sstart + 1)
                    For i = 1 To Sfinish - Sstart + 1
                        vtemp(i) = Sarray(i + Sstart - 1, Sindex)
                    Next i
                End If
        End Select
End Select
GetArraySlice2D = vtemp
Exit Function

ErrHandler:
    Dim M As Integer
    M = MsgBox("Bad Array Input", vbOKOnly, "GetArraySlice2D")

End Function

Below is a fast method to slice Excel variant arrays. Most of this was put together using the info from this excellent site http://bytecomb.com/vba-reference/

Essentially the destination array is pre-built as an empty 1d or 2d variant and passed to the sub with the source array and element index to be sliced. Due to the way arrays are stored in memory it's much faster to slice a column than a row as the memory layout allows a single block to be copied.

The good thing about this is it scales well beyond the Excel row limit.

Option Explicit

#If Win64 Then
    Public Const PTR_LENGTH As Long = 8
    Public Declare PtrSafe Function GetTickCount Lib "kernel32" () As Long
    Public Declare PtrSafe Sub Mem_Copy Lib "kernel32" Alias "RtlMoveMemory" (ByRef Destination As Any, ByRef Source As Any, ByVal Length As Long)
    Private Declare PtrSafe Function VarPtrArray Lib "VBE7" Alias "VarPtr" (ByRef Var() As Any) As LongPtr
    Private Declare PtrSafe Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (Destination As Any, Source As Any, ByVal Length As Long)
    Private Declare PtrSafe Sub FillMemory Lib "kernel32" Alias "RtlFillMemory" (Destination As Any, ByVal Length As Long, ByVal Fill As Byte)
#Else
    Public Const PTR_LENGTH As Long = 4
    Public Declare Function GetTickCount Lib "kernel32" () As Long
    Public Declare Sub Mem_Copy Lib "kernel32" Alias "RtlMoveMemory" (ByRef Destination As Any, ByRef Source As Any, ByVal Length As Long)
    Private Declare Function VarPtrArray Lib "VBE7" Alias "VarPtr" (ByRef Var() As Any) As LongPtr
    Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (Destination As Any, Source As Any, ByVal Length As Long)
    Private Declare Sub FillMemory Lib "kernel32" Alias "RtlFillMemory" (Destination As Any, ByVal Length As Long, ByVal Fill As Byte)
#End If

Private Type SAFEARRAYBOUND
    cElements    As Long
    lLbound      As Long
End Type

Private Type SAFEARRAY_VECTOR
    cDims        As Integer
    fFeatures    As Integer
    cbElements   As Long
    cLocks       As Long
    pvData       As LongPtr
    rgsabound(0) As SAFEARRAYBOUND
End Type

Sub SliceColumn(ByVal idx As Long, ByRef arrayToSlice() As Variant, ByRef slicedArray As Variant)
'slicedArray can be passed as a 1d or 2d array
'sliceArray can also be part bound, eg  slicedArray(1 to 100) or slicedArray(10 to 100)
Dim ptrToArrayVar As LongPtr
Dim ptrToSafeArray As LongPtr
Dim ptrToArrayData As LongPtr
Dim ptrToArrayData2 As LongPtr
Dim uSAFEARRAY As SAFEARRAY_VECTOR
Dim ptrCursor As LongPtr
Dim cbElements As Long
Dim atsBound1 As Long
Dim elSize As Long

    'determine bound1 of source array (ie row Count)
    atsBound1 = UBound(arrayToSlice, 1)
    'get pointer to source array Safearray
    ptrToArrayVar = VarPtrArray(arrayToSlice)
    CopyMemory ptrToSafeArray, ByVal ptrToArrayVar, PTR_LENGTH
    CopyMemory uSAFEARRAY, ByVal ptrToSafeArray, LenB(uSAFEARRAY)
    ptrToArrayData = uSAFEARRAY.pvData
    'determine byte size of source elements
    cbElements = uSAFEARRAY.cbElements

    'get pointer to destination array Safearray
    ptrToArrayVar = VarPtr(slicedArray) + 8 'Variant reserves first 8bytes
    CopyMemory ptrToSafeArray, ByVal ptrToArrayVar, PTR_LENGTH
    CopyMemory uSAFEARRAY, ByVal ptrToSafeArray, LenB(uSAFEARRAY)
    ptrToArrayData2 = uSAFEARRAY.pvData

    'determine elements size
    elSize = UBound(slicedArray, 1) - LBound(slicedArray, 1) + 1
    'determine start position of data in source array
    ptrCursor = ptrToArrayData + (((idx - 1) * atsBound1 + LBound(slicedArray, 1) - 1) * cbElements)
    'Copy source array to destination array
    CopyMemory ByVal ptrToArrayData2, ByVal ptrCursor, cbElements * elSize

End Sub

Sub SliceRow(ByVal idx As Long, ByRef arrayToSlice() As Variant, ByRef slicedArray As Variant)
'slicedArray can be passed as a 1d or 2d array
'sliceArray can also be part bound, eg  slicedArray(1 to 100) or slicedArray(10 to 100)
Dim ptrToArrayVar As LongPtr
Dim ptrToSafeArray As LongPtr
Dim ptrToArrayData As LongPtr
Dim ptrToArrayData2 As LongPtr
Dim uSAFEARRAY As SAFEARRAY_VECTOR
Dim ptrCursor As LongPtr
Dim cbElements As Long
Dim atsBound1 As Long
Dim i As Long

    'determine bound1 of source array (ie row Count)
    atsBound1 = UBound(arrayToSlice, 1)
    'get pointer to source array Safearray
    ptrToArrayVar = VarPtrArray(arrayToSlice)
    CopyMemory ptrToSafeArray, ByVal ptrToArrayVar, PTR_LENGTH
    CopyMemory uSAFEARRAY, ByVal ptrToSafeArray, LenB(uSAFEARRAY)
    ptrToArrayData = uSAFEARRAY.pvData
    'determine byte size of source elements
    cbElements = uSAFEARRAY.cbElements

    'get pointer to destination array Safearray
    ptrToArrayVar = VarPtr(slicedArray) + 8 'Variant reserves first 8bytes
    CopyMemory ptrToSafeArray, ByVal ptrToArrayVar, PTR_LENGTH
    CopyMemory uSAFEARRAY, ByVal ptrToSafeArray, LenB(uSAFEARRAY)
    ptrToArrayData2 = uSAFEARRAY.pvData

    ptrCursor = ptrToArrayData + ((idx - 1) * cbElements)
    For i = LBound(slicedArray, 1) To UBound(slicedArray, 1)

        CopyMemory ByVal ptrToArrayData2, ByVal ptrCursor, cbElements
        ptrCursor = ptrCursor + (cbElements * atsBound1)
        ptrToArrayData2 = ptrToArrayData2 + cbElements
    Next i

End Sub

Example usage:

Sub exampleUsage()
Dim sourceArr() As Variant
Dim destArr As Variant
Dim sliceIndex As Long

    On Error GoTo Err:

    sourceArr = Sheet1.Range("A1:D10000").Value2
    sliceIndex = 2 'Slice column 2 / slice row 2

    'Build target array
    ReDim destArr(20 To 10000) '1D array from row 20 to 10000
'    ReDim destArr(1 To 10000) '1D array from row 1 to 10000
'    ReDim destArr(20 To 10000, 1 To 1) '2D array from row 20 to 10000
'    ReDim destArr(1 To 10000, 1 To 1) '2D array from row 1 to 10000

    'Slice Column
    SliceColumn sliceIndex, sourceArr, destArr

    'Slice Row
    ReDim destArr(1 To 4)
    SliceRow sliceIndex, sourceArr, destArr

Err:
    'Tidy Up See ' http://stackoverflow.com/questions/16323776/copy-an-array-reference-in-vba/16343887#16343887
    FillMemory destArr, 16, 0

End Sub

Timings were on an old dual core CPU using the following test

Sub timeMethods()
Const trials As Long = 10
Const rowsToCopy As Long = 1048576
Dim rng As Range
Dim Arr() As Variant
Dim newArr As Variant
Dim newArr2 As Variant
Dim t As Long, t1 As Long, t2 As Long, t3 As Long
Dim i As Long

    On Error GoTo Err

    'Setup Conditions 1time only
    Sheet1.Cells.Clear
    Sheet1.Range("A1:D1").Value = Split("A1,B1,C1,D1", ",") 'Strings
'    Sheet1.Range("A1:D1").Value = Split("1,1,1,1", ",") 'Longs
    Sheet1.Range("A1:D1").AutoFill Destination:=Sheet1.Range("A1:D" & rowsToCopy), Type:=xlFillDefault

    'Build source data
    Arr = Sheet1.Range("A1:D" & rowsToCopy).Value
    Set rng = Sheet1.Range("A1:D" & rowsToCopy)

    'Build target container
    ReDim newArr(1 To rowsToCopy)
    Debug.Print "Trials=" & trials & " Rows=" & rowsToCopy
    'Range
    t3 = 0
    For t = 1 To trials
        t1 = GetTickCount

            For i = LBound(newArr, 1) To UBound(newArr, 1)
                newArr(i) = rng(i, 2).Value2
            Next i

        t2 = GetTickCount
        t3 = t3 + (t2 - t1)
        Debug.Print "Range: " & t2 - t1
    Next t
    Debug.Print "Range Avg ms: " & t3 / trials

    'Array
    t3 = 0
    For t = 1 To trials
        t1 = GetTickCount

            For i = LBound(newArr, 1) To UBound(newArr, 1)
                newArr(i) = Arr(i, 2)
            Next i

        t2 = GetTickCount
        t3 = t3 + (t2 - t1)
        Debug.Print "Array: " & t2 - t1
    Next t
    Debug.Print "Array Avg ms: " & t3 / trials

    'Index
    t3 = 0
    For t = 1 To trials
        t1 = GetTickCount

            newArr2 = WorksheetFunction.Index(rng, 0, 2) 'newArr2 2d

        t2 = GetTickCount
        t3 = t3 + (t2 - t1)
        Debug.Print "Index: " & t2 - t1
    Next t
    Debug.Print "Index Avg ms: " & t3 / trials

    'CopyMemBlock
    t3 = 0
    For t = 1 To trials
        t1 = GetTickCount

            SliceColumn 2, Arr, newArr

        t2 = GetTickCount
        t3 = t3 + (t2 - t1)
        Debug.Print "CopyMem: " & t2 - t1
    Next t
    Debug.Print "CopyMem Avg ms: " & t3 / trials

Err:
    'Tidy Up
    FillMemory newArr, 16, 0


End Sub