Is it possible to divide a Array in VBA - arrays

Question

Is it possible to divide an Array?
Example:
array(2) As String
array(1) = "test1"
array(2) = "test2"
~ Now Split
array1 (contains test1) & array 2 (contains test2)
I want to implement a Binarysearch

Answer 1

You can split like this
Sub split_array()
Dim array1(1 To 2) As String
Dim array2(1 To 2) As String
Dim array3(1 To 2) As String
array1(1) = "Test1"
array1(2) = "Test2"
array2(1) = array1(1)
array3(1) = array1(2)
End Sub
But I suspect that is not the best way to do it. I think you would do much better using 3 (probably long integer) variables to represent positions in the array. 1 to represent the 1st element, 1 to represent the last element and 1 to represent the mid element.
Dim lLowerSearchElement As Long
Dim lUpperSearchElement As Long
Dim lMiddleSearchElement As Long
Dim array1(1 to 999) as string
lLowerSearchElement = 1
lUpperSearchElement = 999
lMiddleSearchElement = (lUpperSearchElement + lLowerSearchElement) / 2
You can then check if the if the element is equal to, greater or less then the middle element and proceed accordingly.
Also remember that you will need to sort your data before attempting to use a binary search and it would be useful if you know about recursive calling.
You also need to test your implementation rigorously as a small mistake could result in the search not working probably.
Edit 22/08/13
The implementation I use for a binary search is given below:
Function bCheckSamplePoint(ByRef lSamplePointArray() As String, ByRef bfound As Boolean, _
ByVal lSamplePoint As String) As Boolean
'byref used for the array as could be slow to keep copying the array, bFound is used by calling procedure
Dim lLowerSearchElement As Long
Dim lUpperSearchElement As Long
Dim lMiddleSearchElement As Long
bfound = False 'False until found
'Set initial limits of the search
lLowerSearchElement = 0
lUpperSearchElement = UBound(lSamplePointArray())
Do While lLowerSearchElement <= lUpperSearchElement And bfound = False
lMiddleSearchElement = (lUpperSearchElement + lLowerSearchElement) / 2
If StrComp(lSamplePointArray(lMiddleSearchElement), lSamplePoint, vbTextCompare) = -1 Then
' 'Must be greater than middle element
lLowerSearchElement = lMiddleSearchElement + 1
ElseIf (lSamplePointArray(lMiddleSearchElement) = lSamplePoint) Then
bfound = True
Else
'must be lower than middle element
lUpperSearchElement = lMiddleSearchElement - 1
End If 'lSamplePointArray(lmiddlesearchlelemnt) < lSamplePoint
Loop 'While lLowerSearchElement <= lUpperSearchElement
ErrorExit:
bCheckSamplePoint = bReturn
Exit Function
As you can see this binary search is only checking to see wether a string is found in an array of strings, but it could be modified for other purposes.

Answer 2

You don't need a split function to do binary search
My VBA version of binary search can be found at
http://fastexcel.wordpress.com/2011/08/02/developing-faster-lookups-part-3-a-binary-search-udf/

Answer 3

Split Array into chunks
Public Function splitArray(ByVal initial_array As Variant, Optional chunk_size As Long = 1) As Variant()
Dim split_array() As Variant
Dim chunk() As Variant
Dim chunk_index As Integer: chunk_index = 0
Dim array_index As Integer: array_index = 1
If UBound(initial_array) > chunk_size Then
For i = 0 To UBound(initial_array)
If (i + 1) / (chunk_size * array_index) = 1 Or i = UBound(initial_array) Then
ReDim Preserve chunk(chunk_index)
chunk(chunk_index) = initial_array(i)
ReDim Preserve split_array(array_index - 1)
split_array(array_index - 1) = chunk
chunk_index = 0
array_index = array_index + 1
Else
ReDim Preserve chunk(chunk_index)
chunk(chunk_index) = initial_array(i)
chunk_index = chunk_index + 1
End If
Next i
splitArray = split_array
Else
ReDim Preserve split_array(0)
split_array(0) = initial_array
splitArray = split_array
End If
End Function