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sbExactRandInt
Name
sbExactRandInt - Create an exact integer histogram distribution.
Synopsis
sbExactRandInt(vWeight, lDraws)
Description
sbExactRandInt creates Creates an exact histogram distribution for integers (type Long) of vWeight.count draws. vWeight(i) reflects the probability of the occurrence of i. If these weights can't be achieved exactly then the largest remainder method will be applied to minimize the absolute error. If not called as a worksheet function (i.e. via VBA), argument lDraws has to be provided. This function calls (needs) sbRoundToSum.
Options
vWeight Array of weights. Array size determines the number of different classes the range dmin : dmax is divided into. Values in this array specify likelihood of this class' numbers to appear (be drawn).
lDraws Optional - Number of draws. This argument has only to be provided if this function is not called as a worksheet function.
See Also
Please read my Disclaimer.
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Function sbExactRandInt(vWeight As Variant, Optional lDraws As Long = 0) As Variant
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'Creates an exact histogram distribution for vWeight.count draws.
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'vWeight(i) reflects the probability of the occurrence of i.
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'If these weights can't be achieved exactly then the largest remainder method will
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'be applied to minimize the absolute error. This function calls (needs) sbRoundToSum.
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'If not called as a worksheet function (i.e. via VBA), argument lDraws has to be provided.
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'https://berndplumhoff.gitbook.io/sulprobil/excel/excel-vba-solutions/sbexactrandint
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'PB V0.1 02-May-2021 (C) (P) by Bernd Plumhoff
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Static bRandomized As Boolean
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Dim i As Long, j As Long, n As Long, lD As Long
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Dim vW As Variant
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Dim dSumWeight As Double, dR As Double
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If Not bRandomized Then
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Randomize
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bRandomized = True
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End If
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With Application.WorksheetFunction
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vW = .Transpose(vWeight)
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On Error GoTo Errhdl
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i = vW(1) 'Throw error in case of horizontal array
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On Error GoTo 0
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n = UBound(vW)
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lD = lDraws
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If TypeName(Application.Caller) = "Range" Then
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'If called as a worksheet function then the number of selected output cells
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'must equal the number of elements in vWeight and the cell selection must
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'be 1 row or 1 column.
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lD = Application.Caller.Count
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If Application.Caller.Rows.Count <> 1 And Application.Caller.Columns.Count <> 1 Then
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sbExactRandInt = CVErr(xlErrValue)
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Exit Function
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End If
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End If
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If lD < 1 Then
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sbExactRandInt = CVErr(xlErrNum)
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Exit Function
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End If
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ReDim dWeight(1 To n) As Double
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ReDim dSumWeightI(0 To n) As Double
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ReDim vR(1 To lD) As Variant
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For i = 1 To n
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If vW(i) < 0# Then 'A negative weight is an error
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sbExactRandInt = CVErr(xlErrValue)
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Exit Function
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End If
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'Calculate sum of all weights
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dSumWeight = dSumWeight + vW(i)
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Next i
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If dSumWeight = 0# Then
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'Sum of weights has to be greater zero
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sbExactRandInt = CVErr(xlErrValue)
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Exit Function
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End If
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For i = 1 To n
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'Align weights to number of draws
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dWeight(i) = CDbl(lD) * vW(i) / dSumWeight
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Next i
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vW = sbRoundToSum(dWeight, 0)
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On Error GoTo Errhdl
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i = vW(1) 'Throw error in case of horizontal array
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On Error GoTo 0
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For j = 1 To lD
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dSumWeight = 0#
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dSumWeightI(0) = 0#
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For i = 1 To n
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'Calculate sum of all weights
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dSumWeight = dSumWeight + vW(i)
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'Calculate sum of weights till i
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dSumWeightI(i) = dSumWeight
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Next i
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dR = dSumWeight * Rnd
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i = n
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Do While dR < dSumWeightI(i)
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i = i - 1
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Loop
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vR(j) = i + 1
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vW(i + 1) = vW(i + 1) - 1#
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Next j
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sbExactRandInt = vR
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Exit Function
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Errhdl:
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'Transpose variants to be able to address
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'them with vW(i), not vW(i,1)
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vW = .Transpose(vW)
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Resume Next
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End With
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End Function
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Sub Test_sbExactRandInt()
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Dim v As Variant, i As Long, j As Long
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For i = 1 To 10
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v = sbExactRandInt(Array(3, 2, 1), 6)
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For j = 1 To 6
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Debug.Print v(j);
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Next j
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Debug.Print
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Next i
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End Sub
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sbExactRandInt.xlsm
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