Unique Random Number Sequences??

[seagoing]

Anyone now how to, within a self contained function, generate a sequence of UNIQUE random numbers all in a given range?

Based, perhaps, around a call somthing like.....


'************************************************************************
' Paramaters
' NumOfNumbers: Number of unique random numbers to generate
' minRange: Minimum value of any returned random number
' maxRange: Maximum value of any returned random number
' Returns
' randomSequence(): Array of UNIQUE random numbers
'************************************************************************
Public Function getRandomSequence(NumOfNumbers As Integer, minRange As Long, maxRange As Long) As randomSequence()

End Function

[twanvl]

1. You can only generate pseudo random numbers
2. What do you mean unique? Must the sequence be unique? Or the numbers in the sequence?

[seagoing]

The numbers in the sequence need to be unique

[twanvl]

There are two algorithms that I can think of:
- max-min>>numberOfNumbers (much smaller):
    - generate a list, and test each number against the previous numbers in the list, if it is not unique, try again
- else:
    - generate a list of all numbers in the range min...max, randomly shuffle that sequence, and only keep the top n numbers.

[Guv]

The suggested syntax using a Function does not seem valid, although a close approximation could be made with a User Type variable containing an array. The following is a possible alternative.

Dim RandomValue() As Long
. . .
Public Sub RandomArrayFiller(NumOfNumbers As Integer, minRange As Long, _
                                    maxRange As Long)
Redim RandomValue(0 to NumOfNumbers) As Long ‘Value zero for luck. 
Dim TentativeValue As Long
Dim J As Integer
Dim LastRandy As Integer

Randomize  ‘this could be part of Main Line initialize code. 
LastRandy = 0
J = 1
TentativeValue = CLng( minRange + (maxRange - minRange)*Rnd)

Do
       Select Case True
              Case J > LastRandy
                    RandomValue(J) = TentativeValue
                    TentativeValue = CLng(minRange _
                                              + (maxRange - minRange)*Rnd)
                    J = 1
                    LastRandy = LastRandy + 1
              Case TentativeValue = RandomValue(J)
                    TentativeValue = CLng( minRange _
                                           + (maxRange - minRange)*Rnd)
                    J = 1
              Case Else
                    J = J + 1
          End Select

  Loop While LastRandy < NumberOfNumbers

End Sub

Caveat emptor: I neither compiled nor tested the above.

BTW: If you are simulating some random process, it might not be correct to eliminate duplicates.