Filtering 2D Arrays in Excel VBA - arrays

Question

Using Excel and VBA, I wanted some advice on how to best filter data in an array (in the same sort of way one might use a pivot table) strictly using VBA. I am creating a UserForm that is going to make some data decisions based on currently existing data. I can visualize how to do it well enough but am not that versed in VBA programming.
Here is an example
A B C
bob 12 Small
sam 16 Large
sally 1346 Large
sam 13 Small
sally 65 Medium
bob 1 Medium
To grab the data in an Array, I could use
Dim my_array As Variant
my_array = Range("A1").CurrentRegion
Now, I am familiar with looping through 2D arrays, but I wondered: what the most effective way to filter 2D array data (without looping through the array time and again)?
For example, how do I get would be to say get this kind of data:
data_for_sally As Variant 'rows with sally as name in ColA
data_for_sally_less_than_ten As Variant ' all rows with sally's name in ColA and colB < 10
data_for_all_mediums as Variant ' all rows where ColC is Medium
Suggestions? I could work this out with a bunch of custom functions and loops but I thought there must be a better way. Thanks.

Answer 1

I assume you want to use VBA only.
I think it depends on several parameters, mainly on:
how often you run the same condition => do you store the result of a filter or do you recalculate every time?
how often you need to filter stuff => if often, it is worth having a proper code structure in place, if not then a one off loop is clearly the way to go.
From an OO perspective, assuming performance (speed & memory) is not an issue, I would go for the following design (I won't go into the details of the implementation, only give the general idea). Create a class (let's call it imaginatively ArrayFilter) that you could use like this.
Setup the filter
Dim filter As New ArrayFilter
With filter
.name = "sam"
.category = "Medium"
.maxValue = 10
End With
Or
filter.add(1, "sam") 'column 1
filter.add(3, "Medium") 'column 3
filter.addMax(2, 10) 'column 2
Create the filtered data set
filteredArray = getFilteredArray(originalArray, filter)
The getFilteredArray is fairly straightforward to write: you loop over the array checking if the values match the filter and put the valid lines in a new array:
If filter.isValidLine(originalArray, lineNumber) Then 'append to new array
Pros
Clean design
Reusable, especially with the second version where you use the column number. This can be used to filter any arrays really.
Filtering code is in one function that you can test
Corollary: avoid duplication of code
Cons
Filtering is recalculated every time, even if you use the same filter twice. You can store the results in a Dictionary for example - see below.
Memory: every call to the getFilteredArray creates a new array, but not sure how this can be avoided anyway
This adds quite a few lines of code, so I would do it only if it helps make the code easier to read / maintain.
ps: If you need to cache the results to improve performance, one way would be to store the results in a dictionary and add some logic to the getFilteredArray function. Note that unless your arrays are really big and/or you run the same filter a lot, this is probably not worth it.
filters.add filter, filteredArray 'filters is a dictionary
That way, when you call getFilteredArray next time, you can do something like this:
For each f in filters
'Check if all conditions in f and newFilter are the same
'If they are:
getFilteredArray = filters(f)
Exit Function
Next
'Not found in cache: compute the result

Answer 2

Try this
' credited to ndu
Function Filter2DArray(ByVal sArray, ByVal ColIndex As Long, ByVal FindStr As String, ByVal HasTitle As Boolean)
Dim tmpArr, i As Long, j As Long, Arr, Dic, TmpStr, Tmp, Chk As Boolean, TmpVal As Double
On Error Resume Next
Set Dic = CreateObject("Scripting.Dictionary")
tmpArr = sArray
ColIndex = ColIndex + LBound(tmpArr, 2) - 1
Chk = (InStr("><=", Left(FindStr, 1)) > 0)
For i = LBound(tmpArr, 1) - HasTitle To UBound(tmpArr, 1)
If Chk Then
TmpVal = CDbl(tmpArr(i, ColIndex))
If Evaluate(TmpVal & FindStr) Then Dic.Add i, ""
Else
If UCase(tmpArr(i, ColIndex)) Like UCase(FindStr) Then Dic.Add i, "" 'This finds only exact matches, if you need *FindStr* use: If UCase(tmpArr(i, ColIndex)) Like UCase("*" & FindStr & "*") Then Dic.Add i, ""
End If
Next
If Dic.Count > 0 Then
Tmp = Dic.Keys
ReDim Arr(LBound(tmpArr, 1) To UBound(Tmp) + LBound(tmpArr, 1) - HasTitle, LBound(tmpArr, 2) To UBound(tmpArr, 2))
For i = LBound(tmpArr, 1) - HasTitle To UBound(Tmp) + LBound(tmpArr, 1) - HasTitle
For j = LBound(tmpArr, 2) To UBound(tmpArr, 2)
Arr(i, j) = tmpArr(Tmp(i - LBound(tmpArr, 1) + HasTitle), j)
Next
Next
If HasTitle Then
For j = LBound(tmpArr, 2) To UBound(tmpArr, 2)
Arr(LBound(tmpArr, 1), j) = tmpArr(LBound(tmpArr, 1), j)
Next
End If
End If
Filter2DArray = Arr
End Function