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excel vba – Assign 1D array from 2D array in VBA?

Posted by: admin March 9, 2020 Leave a comment

Questions:

So maybe its monday, maybe I’m stupid.. But I can’t for the life of me figure out a good way to get a 1D array from a one row in a 2D array. (maybe it’s not a “real” 2D array?)

Anyways, I have an array that I defined like this: dim myArr(2,4) as variant

I filled it with values 1 – 15 so it looks like:

1,2,3,4,5
6,7,8,9,10
11,12,13,14,15

So now what I want is a single row of that array. the only way I can figure out is by doing this:

    dim temp() as variant
    ReDim temp(lbound(myArr,2) to ubound(myArr,2))

    For i = 0 To 0
        For j = LBound(myArr, 2) To UBound(myArr, 2)
            temp(j) = myArr(i, j)
        Next
    Next

But I don’t like that because if the array got huge, then the time it took to do that might be considerably longer. I THOUGHT I should be able to do:

dim temp as variant
temp = myArr(0) 'since myArr(0) is a 1D array with 5 spots right?

but no.. I get a ‘wrong number of dimentions’ error.

I also dug back through previous things and found this question: How to compare two entire rows in a sheet and the answer by tim thomas shows the use of transpose, and mentions if you were comparing columns you’d use only transpose once, but it doesn’t work.. if I made it like: dim myArr(2,0) as variant the transpose works, but not the way I have it now.

I found countless answers to this question in other languages like C++ and Python but I’m not familiar at all with either so I couldn’t interpret them.

Is there a better way of doing this?
Or am I stuck with this diouble loop that I don’t like?

Thanks!

How to&Answers:

Here’s a self-contained illustration of one way to “slice” a 2-D array:

Sub ArraySlicing()

Dim arr(1 To 5, 1 To 5)
Dim slice
Dim x, y
Dim a As Application

    'Populate a sample 2-D array with values...
    For y = 1 To 5
    For x = 1 To 5
        arr(y, x) = "R" & y & ":C" & x
    Next x
    Next y
    '...done setting up sample array

    Set a = Application 'this is just to shorten the following lines

    'Example 1: get the first "column"
    slice = a.Transpose(a.Index(arr, 0, 1))
    Debug.Print Join(slice, ", ") 'display what we got 

    'Example 2: get second "row" (note double transpose)
    slice = a.Transpose(a.Transpose(a.Index(arr, 2, 0)))
    Debug.Print Join(slice, ", ") 'display what we got

End Sub

Index() gives you a 2-d array – (x,1) or (1,x) – Transpose() will convert that to a 1-d array.

Answer:

Based on Tim Williams’ answer I created a self contained function that will slice out one index of a two-dimensional array and return a one-dimensional array.

Function Slice_String_Array(arr As Variant, dir As Boolean, index As Long) As Variant()
'This function recieves a two-dimensional array, slices one element of it (either a 'column' or a 'row'), and
'returns a one dimensional array with the values.  Both the array passed in the arguments (arr) and the
'returned array are of type Variant.
'

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## 'arr is the two-dimensional array being sliced '"dir" is used for direction, 0 (False) is vertical (column) and 1 (True) is horizontal (column) '"index" is the element number (column number or row number) you want returned '

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## Set a = Application 'this is just to shorten the following lines If dir = 0 Then 'slice a column slice = a.Transpose(a.index(arr, 0, index)) Else 'slice a row slice = a.Transpose(a.Transpose(a.index(arr, index, 0))) End If Slice_String_Array = slice End Function

Answer:

@dathanm: A good initial approach but there are a couple of points that you seem to be unclear about:

  1. In VB, there is no need to explicitly compare Boolean values with zero. The VBA interpreter automatically takes care of that (comparing <> 0, actually, in order to test for a True condition).
  2. (@ Tim Williams too): in your row-slice design, calling the Transpose method is unnecessary because Index returns a 1D array of row values, ready to use as-is. As designed, the two nested Transpose calls are essentially a No-Op. For a full explanation of this, see technical note #3, in the header commentary of my version, below.
  3. The Index method assumes one-based indexing, so your code should check for a passed VB array that is not one-based (very common) and adjust for that case.
  4. A further technicality is that, if the calling code passes a jagged array-of-arrays (not uncommon in VB), the Index method will fail on column operations, so your code should check for that case.
  5. Lastly, it should ensure that the returned sliced-array’s base is the same as the corresponding base of the original 2D array, in the sliced dimension, since that isn’t necessarily the case by default when the Index or Transpose methods are involved.

Here’s my version, for anyone to use as needed:

Function ArraySlice(Arr2D As Variant, ByCol As Boolean, SliceIdx As Long) As Variant ' 'Returns a 1D row or column array "slice" of the specified 2D array. ' 'PARAMETERS: ' ' Arr2D The 2D array from which a row/column slice is to be extracted. The passed array may be of ' any data type. ' ' ByCol True = slice a column; False = slice a row. ' ' SliceIdx The array-index of the row or column to be sliced from the 2D array. Note that the meaning ' of SliceIdx value depends on the base of the 2D array's dimensions: a SliceIdx of 1 will be ' the first row/column of a one-based array but the second row/column of a zero-based array. ' 'RETURN VALUES: If successful, returns a sliced 1D row or column (Variant) array. If unsuccessful, returns ' an Empty Variant status. Note that, though an array of any data type may be passed to this ' routine, the variable receiving the returned array must be a Variant because whole-array ' assignment is implemented for Variants only in VB/VBA. ' 'TECHNICAL NOTES: ' ' 1. IMPORTANT: Though arrays-of-arrays are supported by this routine, jagged arrays-of-arrays (which are ' possible in VBA) would be very complex to handle for column-slice operations, so this routine does not ' support them for that case and will throw an error message accordingly. Also, for column-slice ' operations on rectangular arrays-of-arrays, this routine assumes that each row-array has the same ' LBound (0 or 1 or whatever), which is a condition that can be violated in VB but is extremely unusual. ' This routine will throw an error in that case as well. ' ' 2. The Application.Index method, used by this routine has two forms, an Array form and a Reference form. ' When used by this routine in its Array form, an array (as opposed to a worksheet cell-range reference) ' is passed to it and it returns an array as its return value. In this usage, it doesn't actually ' operate on an Excel worksheet range and is therefore very fast, actually faster than any VBA-coded ' equivalent algorithm, because its functionality is implemented by Excel's underlying compiled-code ' engine. ' ' 3. The Index method and the Transpose method are "orientation-aware" with regard to the row/column ' orientation of the passed array argument. For a multi-row and multi-column rectangular array, the ' orientation question is moot but for a single-row or single-column array it isn't. Without those ' methods' orientation-awareness, they would require an additional optional parameter that the calling ' code would have to set (but only for single-row/column arrays) to inform the methods of the otherwise- ' ambiguous orientation of the passed array. Such a design would further complicate the call interface ' as well as the calling code. ' ' Microsoft's solution was to implement the required orientation-awareness by defining single-row arrays ' as a simple 1D array containing that row's elements (i.e. RowValues(col-num)), and defining single- ' column arrays as a degenerate 2D array containing a single column of each row's value for that column ' (i.e. ColValues(row-num, 1)). That is, those methods determine the orientation of a passed single- ' row/column array by simply checking whether it is a 1D array (row) or 2D array (column). And any ' single-row/column array returned by them also conforms to that scheme. (Technically, it treats the ' passed array as an array-of-arrays, regardless of its implementation in VBA, which is consistent with ' how simple 2D arrays are implemented in C/C++, the language of Excel's compiled-code engine.) ' ' Consequently, to get a true 1D array of column values, the Index method's returned (degenerate) 2D ' array may be passed to the Transpose method, to convert its column-orientation to row-orientation in ' the Transpose method's context. But in the calling-code's context, it becomes just an independent ' 1D array containing the specified column's values. ' 'AUTHOR: Peter Straton ' '************************************************************************************************************* Const NA As Long = 0 Dim Arr1DSlice As Variant 'NOTE: Some slice operations require a subsequent shift of the sliced array's 'base in order to make it match the corresponding base of the original 2D array, 'in the sliced dimension. But, because this function's ArraySlice variable is a 'Variant that's also the function's return value, you can't just use Redim Preserve 'to change its base. Instead, you must us a local (shiftable) Variant and then 'assign that array to the function's return value before returning. Dim BaseOffset As Long Dim ColIdxLBound As Long Dim ColIdxUBound As Long Dim i As Long Dim IndexFncOffset As Long Dim IsArrayOfArrays As Variant 'Variant: can be Empty (undefined) or Boolean Dim RowIdxLBound As Long Dim RowIdxUBound As Long Arr1DSlice = Empty 'Default: failure status 'First, determine whether Arr2D is a 2D array or array-of-arrays because they are processed differently. On Error Resume Next RowIdxLBound = LBound(Arr2D) If Err <> 0 Then Exit Function 'Not an array, so exit with failure status RowIdxUBound = UBound(Arr2D) IsArrayOfArrays = IsArray(Arr2D(RowIdxLBound, RowIdxLBound)) If IsEmpty(IsArrayOfArrays) Then IsArrayOfArrays = IsArray(Arr2D(RowIdxLBound)) On Error GoTo 0 'Do the slice operation With Application If ByCol Then If IsArrayOfArrays Then ColIdxLBound = LBound(Arr2D(RowIdxLBound)) 'Assumes consistent column-index LBounds and UBounds for ColIdxUBound = UBound(Arr2D(RowIdxLBound)) 'each row in the array-of-arrays, but... 'Ensure that it doesn't have inconsistent column-index LBounds and isn't a jagged array-of-arrays '(neither of which are supported) by checking each row's column-index bounds. For i = RowIdxLBound To RowIdxUBound If LBound(Arr2D(i)) <> ColIdxLBound Then MsgBox "Arr1DSlice: Arrays-of-arrays with inconsistent column-index LBounds are not " & _ "supported for column operations.", vbOKOnly + vbCritical, "PROGRAMMING ERROR" Exit Function End If If UBound(Arr2D(i)) <> ColIdxUBound Then MsgBox "Arr1DSlice: Jagged arrays-of-arrays are not supported for column operations.", _ vbOKOnly + vbCritical, "PROGRAMMING ERROR" Exit Function End If Next i Else 'Standard 2D array ColIdxLBound = LBound(Arr2D, 2) ColIdxUBound = UBound(Arr2D, 2) End If If ColIdxLBound > SliceIdx Then 'If the specified slice-index isn't in-bounds, clip it accordingly SliceIdx = ColIdxLBound ElseIf ColIdxUBound < SliceIdx Then SliceIdx = ColIdxUBound End If IndexFncOffset = 1 - ColIdxLBound 'The Index method assumes one-based indexing, so must adjust for 'non-one-based arrays when that is the case. Arr1DSlice = .index(Arr2D, NA, SliceIdx + IndexFncOffset) 'Returns a degenerate 2D array of a single 'column's corresponding row values (see TECHNICAL NOTE #3, above), 'so must... Arr1DSlice = .Transpose(Arr1DSlice) '...use Transpose to convert it to a 1D array (technically a "row" 'array in the Transpose method's context but is actually just an 'independent 1D array in this context). 'Determine whether the row-dimension base of the original 2D array is different from the base of the 'resulting sliced array (which is necessarily one-based when generated by the Index method), in order to 'fix it if necessary, below. NOTE: the column being sliced from the original 2D array is indexed by its 'row-position index values, therefore it is the 2D array's row-dimension that must be checked for possible 'adjustment of the column-sliced 1D array. BaseOffset = 1 - RowIdxLBound Else 'ByRow If RowIdxLBound > SliceIdx Then 'If the specified slice-index isn't in-bounds, clip it accordingly SliceIdx = RowIdxLBound ElseIf RowIdxUBound < SliceIdx Then SliceIdx = RowIdxUBound End If If IsArrayOfArrays Then Arr1DSlice = Arr2D(SliceIdx) 'For array-of-arrays, just return the SliceIdx row of the 2D array 'NOTE: The Index method is not used here so there is no need to check for an array-base adjustment. Else 'Standard 2D array IndexFncOffset = 1 - RowIdxLBound 'The Index method assumes one-based indexing, so must adjust for 'non-one-based arrays when that is the case. Arr1DSlice = .index(Arr2D, SliceIdx + IndexFncOffset, NA) 'Slice out the SliceIdx row 'NOTE: in the row-slice case, there is no need to transpose (from column array to row array). 'Determine whether the column-dimension base of the original 2D array is different from the base of 'the resulting sliced array (which is necessarily one-based when generated by the Index method), in 'order to fix it if necessary (below). NOTE: the row being sliced from the original 2D array is 'indexed by its column-position index values, therefore it is the 2D array's column-dimension that 'must be checked for possible adjustment of the row-sliced 1D array. BaseOffset = 1 - LBound(Arr2D, 2) '(Is never an array-of-arrays here!) End If End If If BaseOffset <> 0 Then 'The base of the original 2D array is different from the base of the resulting sliced array, so fix the 'sliced array to match the original. ReDim Preserve Arr1DSlice(LBound(Arr1DSlice) - BaseOffset To UBound(Arr1DSlice) - BaseOffset) End If End With 'Application ArraySlice = Arr1DSlice '(See the technical note at the Arr1DSlice variable's declaration) End Function 

And, here’s a handy test routine with which to play with it:

Sub ArraySliceTest() Dim ByCol As Boolean Dim ColIdxLBound As Long Dim ColIdxUBound As Long Dim i As Long Dim j As Long Dim n As Long Dim m As Long Dim PadTabs As String Dim RowIdxLBound As Long Dim RowIdxUBound As Long Dim Sliced As Variant Dim SliceIdx As Long Dim TempBuf1 As Variant Dim TempBuf2 As String Dim TestArr() As Variant #Const Std2DArray = True 'For array-of-arrays, set to False #Const JaggedArray = False 'For jagged array-of-arrays, set to True ' ByCol = True 'Uncomment for column slice ByCol = False 'Uncomment for row slice ' SliceIdx = -1 'Uncomment slice-index value to be tested... ' SliceIdx = 0 ' SliceIdx = 1 SliceIdx = 2 ' SliceIdx = 3 ' SliceIdx = 4 #If Std2DArray Then ' ReDim TestArr(0 To 2, 0 To 3) 'Uncomment test-array dimensions to be tested... ' ReDim TestArr(1 To 3, 1 To 4) ReDim TestArr(-1 To 1, -1 To 2) ' ReDim TestArr(0 To 2, 1 To 4) ' ReDim TestArr(0 To 2, -1 To 2) ' ReDim TestArr(1 To 3, 0 To 3) ' ReDim TestArr(-1 To 1, 0 To 3) RowIdxLBound = LBound(TestArr, 1) RowIdxUBound = UBound(TestArr, 1) ColIdxLBound = LBound(TestArr, 2) ColIdxUBound = UBound(TestArr, 2) 'To demonstrate Variant flexibility, use integers for 2D array For i = RowIdxLBound To RowIdxUBound n = n + 1 m = 0 '(Re)init TempBuf1 = vbNullString For j = ColIdxLBound To ColIdxUBound m = m + 1 TestArr(i, j) = n * 10 + m Next j Next i #Else 'For array-of-arrays: 'To demonstrate Variant flexibility, use strings for array-of-arrays #If Not JaggedArray Then TestArr = Array(Array("11", "12", "13", "14"), _ Array("21", "22", "23", "24"), _ Array("31", "32", "33", "34")) 'Creates an array of arrays. #Else TestArr = Array(Array("11", "12", "13", "14"), _ Array("21", "22"), _ Array("31", "32", "33", "34")) 'Creates a jagged array of arrays. #End If 'Test inconsistent col-index LBounds for all rows in an array-of-arrays (unsupported for col slice) ' Dim X As Variant ' #If JaggedArray Then ' X = Array("21", "22") ' #Else ' X = Array("21", "22", "23", "24") ' #End If ' ' ReDim Preserve X(LBound(X) - 1 To UBound(X) - 1) ' TestArr(2) = X 'Test array-of-arrays col-index LBounds other than the default (supported for row & col slice) ' Dim X As Variant ' Dim Y As Variant ' Dim Z As Variant ' X = Array("11", "12", "13", "14") ' ReDim Preserve X(LBound(X) + 1 To UBound(X) + 1) ' Y = Array("21", "22", "23", "24") ' ReDim Preserve Y(LBound(Y) + 1 To UBound(Y) + 1) ' Z = Array("31", "32", "33", "34") ' ReDim Preserve Z(LBound(Z) + 1 To UBound(Z) + 1) ' ReDim TestArr(0 To 2) ' TestArr(0) = X ' TestArr(1) = Y ' TestArr(2) = Z RowIdxLBound = LBound(TestArr) RowIdxUBound = UBound(TestArr) ColIdxLBound = LBound(TestArr(RowIdxLBound)) 'Assumes consistent column-index LBounds and UBounds for ColIdxUBound = UBound(TestArr(RowIdxLBound)) 'each row in the array-of-arrays (and is used accordingly 'below). #End If 'Std2DArray 'Print the 2D test array Debug.Print vbLf & "+--- " & IIf(ByCol, "Col", "Row") & " Slice ---+" TempBuf1 = vbTab TempBuf2 = vbTab For j = ColIdxLBound To ColIdxUBound TempBuf1 = TempBuf1 & Format(j, IIf(j >= 0, " 0", "#0")) & vbTab TempBuf2 = TempBuf2 & ".." & vbTab Next j Debug.Print Trim$(TempBuf1) Debug.Print Trim$(TempBuf2) For i = RowIdxLBound To RowIdxUBound TempBuf1 = vbNullString #If Std2DArray Then For j = ColIdxLBound To ColIdxUBound TempBuf1 = TempBuf1 & TestArr(i, j) & vbTab Next j #Else For j = LBound(TestArr(i)) To UBound(TestArr(i)) 'Handles jagged array-of-arrays TempBuf1 = TempBuf1 & TestArr(i)(j) & vbTab Next j #End If Debug.Print Format(i, IIf(i >= 0, " 0", "#0")) & ":" & vbTab & Trim$(TempBuf1) Next i 'Get the slice Sliced = ArraySlice(Arr2D:=TestArr, ByCol:=ByCol, SliceIdx:=SliceIdx) If Not IsEmpty(Sliced) Then 'Succeeded, so print the 1D slice array PadTabs = String(SliceIdx - LBound(Sliced), vbTab) Debug.Print If ByCol Then ' Debug.Print vbTab & PadTabs & Format(SliceIdx, IIf(SliceIdx >= 0, " 0", "#0")) ' Debug.Print vbTab & PadTabs & ".." For i = LBound(Sliced) To UBound(Sliced) Debug.Print Format(i, IIf(i >= 0, " 0", "#0")) & ": " & PadTabs & Sliced(i) Next i Else TempBuf1 = Format(SliceIdx, IIf(SliceIdx >= 0, " 0", "#0")) & ":" & vbTab For i = LBound(Sliced) To UBound(Sliced) TempBuf1 = TempBuf1 & Sliced(i) & vbTab Next i Debug.Print TempBuf1 End If Else MsgBox "The ArraySlice function call failed" End If Debug.Print "+-----------------+" End Sub 

Answer:

 Public Function VectorizeArrayCols(Arr As Variant) As Variant Dim n, nn, n3, k As Long n = UBound(Arr, 1) nn = UBound(Arr, 2) 'n = Arr.Columns.Count 'if Public Function Vectorize(Arr As Range) As String 'nn = Arr.Rows.Count 'if Public Function Vectorize(Arr As Range) As String n3 = n * nn Dim Vx() As Variant ReDim Vx(n3) For i = 1 To n For j = 1 To nn k = i + n * (j - 1) Vx(k) = Arr(i, j) Next j Next i VectorizeArrayCols = Vx End Function