Improved line sort

This article was contributed by Chad

These macros offer several improvements over the bubblesort
line sorting macro
submitted by Harald Mueller.

The improvements include:

  1. The sorting is done off-screen in an array, which boosts
    the speed tremendously. Mueller’s sorting implementation
    "bubbles" the lines directly in the file, so
    the bottleneck of his macro is in screen redrawing, not
    in his choice of algorithm.
  2. The algorithm used is QuickSort, which has O(n log n)
    complexity. Mueller uses BubbleSort, which has O(n^2)
  3. This implementation allows you to ignore case when
  4. This implementation allows you to ignore leading and
    trailing whitespace when sorting.

Mueller’s implementation also contains a bug that occurs when
you have chosen to disable editing of read-only files and you try
to sort a read-only file. Since he does not build an internal
representation of the lines (he sorts right in the document), the
lines in the read-only file are never put in the correct order,
and the sorting loop never exits.

That having been said, Mueller’s implementation has some
advantages over mine:

  1. His implementation should handle arbitrarily large
    selections because he does not store all the lines in
    memory. My implementation will fail for large selections,
    because it tries to store the entire selection in memory.
    I have verified that my implementation seems to fail with
    selections of around 500 lines. I don’t know whether this
    is because of an array size limitation or whether it is
    dependent on the length (in bytes) of the selection.
  2. With Mueller’s approach, one can see the bubble sorting
    happening on the screen, which is rather entertaining
    and, for intro-Comp. Sci majors, edifying.

Without further ado, here is the code. There are three

  • CollectLines, which takes a selection and returns a
    VBScript array containing all the lines of the selection.
  • QuickSort, which takes an array and some bounds and sorts
    the array recursively.
  • SortLines, which is the framework that does some
    verification on the document and then calls CollectLines
    and QuickSort, and then rewrites the sorted output.

Function CollectLines(Selection)
 '-- make sure the top of the selection is really the top
 StartLine = Selection.TopLine
 EndLine = Selection.BottomLine
 If EndLine < StartLine Then
 End If
 Dim lines() '-- don't try to collect an empty selection
 If StartLine > EndLine Then
   Redim lines(0)
   CollectLines = lines
   Exit Function
 End If

 '-- collect all the lines of the selection into an array
 '-- this could be prohibitive on large selections ( > 2M ? )
 Redim lines(EndLine - StartLine)
 For i = StartLine To EndLine > Selection.GoToLine i
 lines(endLine - i) = Selection.Text

 CollectLines = lines
End Function

'-- An internal routine To sort an array
'-- Specify ignoreWhiteSpace = True To ignore leading and trailing whitespace
'-- Specify ignoreCase = True To compare strings ignoring case

Sub QuickSort(vec,loBound,hiBound,ignoreWhiteSpace,ignoreCase)
 Dim pivot,loSwap,hiSwap,temp

 '-- This procedure is adapted from the algorithm given in:
 '--    Data Abstractions & Structures using C++ by
 '--    Mark Headington and David Riley, pg. 586

 '-- two items To sort
 If hiBound - loBound = 1 Then
    If vec(loBound) > vec(hiBound) Then
       vec(loBound) = vec(hiBound)
       vec(hiBound) = temp
    End If
 End If

 '-- three or more items To sort
 pivot = vec(int((loBound + hiBound) / 2))
 vec(int((loBound + hiBound) / 2)) = vec(loBound)
 vec(loBound) = pivot
 loSwap = loBound + 1
 hiSwap = hiBound

 '-- find the correct loSwap
 vecLoSwap = vec(loSwap)
 If (ignoreCase = 1 And ignoreWhitespace = 1) Then
    While loSwap < hiSwap and ucase(trim(vec(loSwap))) <= ucase(trim(pivot))
        loSwap = loSwap + 1
 Elseif (ignoreCase = 1) Then
    While loSwap < hiSwap and ucase(vec(loSwap)) <= ucase(pivot)
        loSwap = loSwap + 1
 Elseif (ignoreWhiteSpace = 1) Then
    While loSwap < hiSwap and trim(vec(loSwap)) <= trim(pivot)
         loSwap = loSwap + 1
    While loSwap < hiSwap and vec(loSwap) <= pivot
         loSwap = loSwap + 1
 End If

 '-- find the correct hiSwap
 If (ignoreCase = 1 And ignoreWhitespace = 1) Then
 While ucase(trim(vec(hiSwap))) > ucase(trim(pivot))
     hiSwap = hiSwap - 1
 Elseif (ignoreCase = 1) Then
 While ucase(vec(hiSwap)) > ucase(pivot)
    hiSwap = hiSwap - 1
 Elseif (ignoreWhiteSpace = 1) Then
 While trim(vec(hiSwap)) > trim(pivot)
    hiSwap = hiSwap - 1
 While vec(hiSwap) > pivot
    hiSwap = hiSwap - 1
 End If

 '-- swap values if out of order
 If loSwap < hiSwap Then
 temp = vec(loSwap)
 vec(loSwap) = vec(hiSwap)
 vec(hiSwap) = temp
 End If
 loop While loSwap < hiSwap

 vec(loBound) = vec(hiSwap)
 vec(hiSwap) = pivot

 '-- Recursively sort the partitions

 '-- if there are 2 or more items in first partitions
 If loBound < (hiSwap - 1) Then
 Call QuickSort(vec,loBound,hiSwap-1,ignoreWhiteSpace, ignoreCase)
 End If

 '-- 2 or more items in second section
 If hiSwap + 1 < hibound Then
 Call QuickSort(vec,hiSwap+1,hiBound, ignoreWhiteSpace, ignoreCase)
 End If

End Sub

Sub SortLines
'DESCRIPTION: Sorts the selected lines
 If ActiveDocument.Type <> "Text" Then
    MsgBox "This macro can only be run when a text editor window is active."
 Exit Sub
 End If

 '-- make sure the top of the selection is really the top
 StartLine = ActiveDocument.Selection.TopLine
 EndLine = ActiveDocument.Selection.BottomLine
 If EndLine < StartLine Then
 Temp = StartLine
 StartLine = EndLine
 EndLine = Temp
 End If

 '-- collect the lines of the selection into an array
 lines = CollectLines(ActiveDocument.Selection)

 If isnull(lines) Then
 Exit Sub
 End If

 If (ubound(lines) <= 0) Then
    '-- don't try to sort an empty selection
    Exit Sub
 End If

 '-- sort the array
 Call QuickSort (lines, lbound(lines), ubound(lines), 0, 0)

 '-- select the entire original selection, then delete it
 ActiveDocument.Selection.GoToLine StartLine

 ActiveDocument.Selection.LineDown dsExtend, (EndLine - StartLine) + 1

 '-- write the sorted lines out to the file
 For i = 0 To EndLine - StartLine
 ActiveDocument.Selection = lines(i)
End Sub

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