A format for expressing an ordered list of integers is to use a comma separated list of either

 individual integers
 Or a range of integers denoted by the starting integer separated from the end integer in the range by a dash, '-'. (The range includes all integers in the interval including both endpoints)
 The range syntax is to be used only for, and for every range that expands to more than two values.
Example

The list of integers:

 -6, -3, -2, -1, 0, 1, 3, 4, 5, 7, 8, 9, 10, 11, 14, 15, 17, 18, 19, 20
Is accurately expressed by the range expression:

 -6,-3-1,3-5,7-11,14,15,17-20
(And vice-versa).

Task

 Create a function that takes a list of integers in increasing order and returns a correctly formatted string in the range format. 
 Use the function to compute and print the range formatted version of the following ordered list of integers. (The correct answer is: 0-2,4,6-8,11,12,14-25,27-33,35-39).


    0,  1,  2,  4,  6,  7,  8, 11, 12, 14,
   15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
   25, 27, 28, 29, 30, 31, 32, 33, 35, 36,
   37, 38, 39

 Show the output of your program.


Related task

   Range expansion


 
Public Function RangeExtraction(AList) As String
'AList is a variant that is an array, assumed filled with numbers in ascending order
Const RangeDelim = "-"          'range delimiter
Dim result As String
Dim InRange As Boolean
Dim Posn, ub, lb, rangestart, rangelen As Integer
 
result = ""
'find dimensions of AList
ub = UBound(AList)
lb = LBound(AList)
Posn = lb
While Posn < ub
  rangestart = Posn
  rangelen = 0
  InRange = True
  'try to extend the range
  While InRange
    rangelen = rangelen + 1
    If Posn = ub Then
      InRange = False
    Else
      InRange = (AList(Posn + 1) = AList(Posn) + 1)
      Posn = Posn + 1
    End If
  Wend
  If rangelen > 2 Then 'output the range if it has more than 2 elements
    result = result & "," & Format$(AList(rangestart)) & RangeDelim & Format$(AList(rangestart + rangelen - 1))
  Else 'output the separate elements
    For i = rangestart To rangestart + rangelen - 1
      result = result & "," & Format$(AList(i))
    Next
  End If
  Posn = rangestart + rangelen
Wend
RangeExtraction = Mid$(result, 2) 'get rid of first comma!
End Function
 
 
Public Sub RangeTest()
'test function RangeExtraction
'first test with a Variant array
Dim MyList As Variant
MyList = Array(0, 1, 2, 4, 6, 7, 8, 11, 12, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 27, 28, 29, 30, 31, 32, 33, 35, 36, 37, 38, 39)
Debug.Print "a) "; RangeExtraction(MyList)
 
'next test with an array of integers
Dim MyOtherList(1 To 20) As Integer
MyOtherList(1) = -6
MyOtherList(2) = -3
MyOtherList(3) = -2
MyOtherList(4) = -1
MyOtherList(5) = 0
MyOtherList(6) = 1
MyOtherList(7) = 3
MyOtherList(8) = 4
MyOtherList(9) = 5
MyOtherList(10) = 7
MyOtherList(11) = 8
MyOtherList(12) = 9
MyOtherList(13) = 10
MyOtherList(14) = 11
MyOtherList(15) = 14
MyOtherList(16) = 15
MyOtherList(17) = 17
MyOtherList(18) = 18
MyOtherList(19) = 19
MyOtherList(20) = 20
Debug.Print "b) "; RangeExtraction(MyOtherList)
End Sub
 