How can I randomly select a number of cells and display the contents in a message box?

Question

I have a list of ID numbers 1101-1137 in cells A1-A37. I would like to click a button to randomly select 20 of these, with no repetitions, and display them in a message box.

Answer 1

Just shuffle the indices:

Sub MAIN()
   Dim ary(1 To 37) As Variant
   Dim i As Long, j As Long

   For i = 1 To 37
      ary(i) = i
   Next i

   Call Shuffle(ary)

   msg = ""
   For i = 1 To 20
      j = ary(i)
      msg = msg & vbCrLf & Cells(j, 1).Value
   Next i
   MsgBox msg
End Sub



Public Sub Shuffle(InOut() As Variant)
    Dim i As Long, j As Long
    Dim tempF As Double, Temp As Variant

    Hi = UBound(InOut)
    Low = LBound(InOut)
    ReDim Helper(Low To Hi) As Double
    Randomize

    For i = Low To Hi
        Helper(i) = Rnd
    Next i


    j = (Hi - Low + 1) \ 2
    Do While j > 0
        For i = Low To Hi - j
          If Helper(i) > Helper(i + j) Then
            tempF = Helper(i)
            Helper(i) = Helper(i + j)
            Helper(i + j) = tempF
            Temp = InOut(i)
            InOut(i) = InOut(i + j)
            InOut(i + j) = Temp
          End If
        Next i
        For i = Hi - j To Low Step -1
          If Helper(i) > Helper(i + j) Then
            tempF = Helper(i)
            Helper(i) = Helper(i + j)
            Helper(i + j) = tempF
            Temp = InOut(i)
            InOut(i) = InOut(i + j)
            InOut(i + j) = Temp
          End If
        Next i
        j = j \ 2
    Loop
End Sub