Random Sampling & Selection by Category VBA - vba

Question

I am trying to write a macro on MS Excel, which will enable me to create random samples and pick random values from those samples for each category in the data.
To be more specific, the data is at 2 levels: firm and year, where each row represents a firm-year-peer observation. For each firm i, at a given year j, we have number of actual peers.
What I want to do is assign to each firm, from the whole sample throughout many years, a random firm from the list of all available firms at that specific year. The trick is that the number of firms to be assigned should be identical to the number of actual peers that a firm has at that year. Also, the randomly assigned values should be different from the firm's actual peers, and of course, the firm itself.
i j k
1 2006 100
1 2006 105
1 2006 110
2 2006 113
2 2006 155
2 2006 200
2 2006 300
For example, Firm 1's actual peers in year 2006 are 100, 105 and 110. However, all possible firms available are 100, 105, 110, 113, 155, 200 and 300. This means that I have to select 3 (because Firm 1 has 3 actual peers) random fictional peers from the 4 firms that are not Firm 1's peer that year (i.e. 113, 155, 200 and 300). Applying the same procedure for Firm 2, I need to select 4 random firms that are not Firm 2's actual peers from all possible firms.
I hope this was clear.
I started trying this function out on MS Excel, but I am open to suggestions if you think other platforms would be more useful.
Your help would be very much appreciated!
Thanks!

Answer 1

Many thanks to everyone who has visited my post.
After some initial struggling, I have managed to figure out the code myself. I am posting it below for anyone who might need it.
Basically I used the randomisation code posted by this gentle soul, and enhanced it for my needs using couple of flags for each new firm and each new year. Hope it is clear for everyone.
Best
Sub Random_Sampling()
'
Dim PeerCount, FirmCount, YearCount As Long
Dim Focal_CIK, fiscalYear As Long
Const nItemsTotal As Long = 1532
Dim rngList As Range
Dim FirmYearRange As Range
Dim FirmStart, FirmStartRow, YearStartRow As Long
Dim ExistingPeers As Range
Dim idx() As Long
Dim varRandomItems() As Variant
Dim i, j, k, m, n As Long
Dim iCntr, jCntr As Long
Dim booIndexIsUnique As Boolean
Set rngList = Sheets("Sheet2").Range("A2").Resize(nItemsTotal, 1)
FirmCount = Cells(2, 10).Value
For k = 1 To FirmCount
FirmStart = Application.WorksheetFunction.Match(k, Columns("E"), 0)
Focal_CIK = Cells(FirmStart, 1).Value
YearCount = Cells(FirmStart, 7).Value
For m = 1 To YearCount
Set FirmYearRange = Range("H" & FirmStart & ":H200000")
YearStartRow = Application.WorksheetFunction.Match(m, FirmYearRange, 0) + FirmStart - 1
fiscalYear = Cells(YearStartRow, 3).Value
PeerCount = Cells(YearStartRow, 9).Value
Set ExistingPeers = Range(Cells(YearStartRow + PeerCount, 2), Cells(YearStartRow + PeerCount, 2))
ReDim idx(1 To PeerCount)
ReDim varRandomItems(1 To PeerCount)
For i = 1 To PeerCount
Do
booIndexIsUnique = True ' Innoncent until proven guilty
idx(i) = Int(nItemsTotal * Rnd + 1)
For j = 1 To i - 1
If idx(i) = idx(j) Then 'Is already picked
ElseIf idx(i) = Focal_CIK Then 'Is the firm itself
booIndexIsUnique = False 'If true, don't pick it
Exit For
End If
For n = 1 To PeerCount
If idx(i) = Cells(YearStartRow + n - 1, 2).Value Then 'Is one of the actual peers
booIndexIsUnique = False 'If true, don't pick it
Exit For
Exit For
End If
Next n
Next j
If booIndexIsUnique = True Then
Exit Do
End If
Loop
varRandomItems(i) = rngList.Cells(idx(i), 1)
Rows(YearStartRow + PeerCount).EntireRow.Insert
'The order of the columns are very important for the following lines
Cells(YearStartRow + PeerCount, 1) = Focal_CIK
Cells(YearStartRow + PeerCount, 2) = varRandomItems(i)
Cells(YearStartRow + PeerCount, 3) = fiscalYear
Cells(YearStartRow + PeerCount, 4) = "0"
Next i
Next m
Next k
End Sub