Sorting Arrays or collections - vba

Question

I have the following code as a sub in Excel 2010:
i = 2
For j = 1 To num_scenarios
Dim probdiff As Double
Dim OCS_Spend As Double
n = 0
For k = 1 To num_yrs
' These are the calculations and potentially not relevant to my question but here for context
For Each cell In rng
x = Rnd()
'Debug.Print Format(x, "0.00000%")
If cell.Value >= x Then
'Populate the result sheet
Sheets("Event Occurs").Cells(i, 1) = mywksht.Cells(cell.Row, 1)
Sheets("Event Occurs").Cells(i, 2) = mywksht.Cells(cell.Row, 2)
Sheets("Event Occurs").Cells(i, 3) = mywksht.Cells(cell.Row, 3)
Sheets("Event Occurs").Cells(i, 4) = mywksht.Cells(cell.Row, 4)
Sheets("Event Occurs").Cells(i, 5) = mywksht.Cells(cell.Row, 5)
Sheets("Event Occurs").Cells(i, 6) = mywksht.Cells(cell.Row, 6)
Sheets("Event Occurs").Cells(i, 10) = "Event Occurs"
Sheets("Event Occurs").Cells(i, 11) = mywksht.Cells(cell.Row, 11)
Sheets("Event Occurs").Cells(i, 9) = x
Sheets("Event Occurs").Cells(i, 7) = k
Sheets("Event Occurs").Cells(i, 8) = j
Sheets("Event Occurs").Cells(i, 14) = (cell.Value - x) ^ (2)
event_max = Sheets("Event Occurs").Cells(i, 11)
probdiff = probdiff + (cell.Value - x) ^ (2)
If Round(cell / x, 0) >= event_max Then
Sheets("Event Occurs").Cells(i, 12) = event_max
Else
Sheets("Event Occurs").Cells(i, 12) = Round(cell / x, 0)
End If
Duration = Sheets("Event Occurs").Cells(i, 4)
Num_Event = Sheets("Event Occurs").Cells(i, 12)
Spend = Sheets("Event Occurs").Cells(i, 5)
Sheets("Event Occurs").Cells(i, 13) = Num_Event * Spend / Duration
OCS_Spend = OCS_Spend + Num_Event * Spend / Duration
n = n + 1
i = i + 1
End If
Next cell
' End calculations
Next k
Debug.Print j, probdiff / n
probdiff = 0
OCS_Spend = 0
Next j
The output to the immediate window looks like this:
J: MSE:
1 0.194236476623154
2 0.157939130921924
3 0.19825548826238
4 0.384990330451172
5 0.267128221022187
The first column is j (the outer for loop) and represents a scenario. The second column is the mean square error of the data generated by each iteration of the outer j loop. So 1 is the first time the loop runs,2 is the second etc.. The smaller the number in column MSE, the more likely the scenario is to occur.
I want people to be able to limit the number of scenarios (j's) they see to only the most likely in the event they want to run 100 scenarios. So I need a way of sorting the table above to something like this
j: MSE
2 0.157939130921924
1 0.194236476623154
3 0.19825548826238
5 0.267128221022187
4 0.384990330451172
And if someone wanted to see only the top three results, it would be this:
j: MSE
2 0.157939130921924
1 0.194236476623154
3 0.19825548826238
So basically the three most likely out of 5 possible scenarios. I have tried collections and arrays but not dicitonaries (I am still learning how to use these and not sure if they exists in Excel VBA).

Answer 1

Chip Pearson provides a number of very useful functions which can sort arrays, collections, and dictionaries, which are available here:
http://www.cpearson.com/Excel/SortingArrays.aspx
There is too much code there to reproduce here. What I typically do when the need arises is to create a separate module in my VBProject which contains these array helper functions. I have used these extensively in PowerPoint and they worked in that environment with minimal modifications. For Excel, they should work out-of-the-box.
Once you have put the data in an array (I don't see any arrays in your code, so let's assume you have something like Dim MyArray As Variant), and sorted it using those functions, you can do something like this to cut the array down to include only the first x results:
'where "x" is a long/integer represents some user-input or _
limit to the number of results:
ReDim Preserve MyArray(x - 1)
I would use arrays rather than collections or dictionaries.
Why not Collections? Collections are useful and would arguably do the job, here. However, whereas we can "resize" the array in a single ReDim Preserve statement, you cannot do that with a Collection object; you would instead have to use iteration. While this is not overly complicated, it does seem a bit clunkier. (You could of course do some tests on performance, but unless you are dealing with very large sets of data, I would not expect a noticeable gain either way).
Sub testCollection()
Dim coll As New Collection
Dim i As Integer
For i = 1 To 10
coll.Add i
Next
Dim x As Integer 'The maximum number of results you want to return:
x = 4
Do Until coll.Count = x
coll.Remove (coll.Count)
Loop
End Sub
Why not dictionaries? While a dictionary's .Keys returns a one-dimensional array of values, in order to avoid iteration (like in the collection object) you would still need to transfer these to an array:
MyArray = dict.Keys()
ReDim Preserve MyArray(x-1)
Further, the dictionary object holds unique key values, so these are not good to use if you anticipate that there may be duplicate values that you need to store.

Answer 2

One option is to use a System.Collections.ArrayList since this object directly supports a Sort method. The Object is "borrowed" from VB.NET.
EDIT#1
Here is a sample:
Sub SortDemo()
s = Array("Larry", "Moe", "Curley", "Manny", "Zack", "Jack")
L = LBound(s)
U = UBound(s)
With CreateObject("System.Collections.ArrayList")
For k = L To U
.Add s(k)
Next k
.Sort
s = .toarray
End With
msg = ""
For k = L To U
msg = msg & s(k) & vbCrLf
Next k
MsgBox msg
End Sub
and here are the references in place:
For more information see:
Ozgrid Material