NoNdxShSort

Sub ShellSort(arr As Variant, Optional lastEl As Variant, _
Optional descending As Boolean)
Dim value As Variant
Dim index As Long, index2 As Long
Dim firstEl As Long
Dim distance As Long
Dim numEls As Long

' account for optional arguments

If IsMissing(lastEl) Then lastEl = UBound(arr)
firstEl = LBound(arr)

numEls = lastEl - firstEl + 1
' find the best value for distance

Do
distance = distance * 3 + 1
Loop Until distance > numEls

Do
distance = distance \ 3
For index = distance + firstEl To lastEl
value = arr(index)
index2 = index
Do While (arr(index2 - distance) > value) Xor descending
arr(index2) = arr(index2 - distance)
index2 = index2 - distance
If index2 - distance < firstEl Then Exit Do
Loop
arr(index2) = value
Next
Loop Until distance = 1
End Sub


ShellSort an array of any type

ShellSort behaves pretty well with arrays of any size, even
if the array is already "nearly-sorted", even though in
particular cases BubbleSort or QuickSort can be more efficient.

LASTEL is the index of the last item to be sorted, and is
useful if the array is only partially filled. This updated
version accounts for arrays whose LBound is 0 and 1
(or whatever)

Works with any kind of array, except UDTs and fixed-length
strings, and including objects if your are sorting on their
default property. String are sorted in case-sensitive mode.

You can write faster procedures if you modify the first two lines
to account for a specific data type, eg.

' Sub ShellSortS(arr() As Single, Optional lastEl As Variant,

' Optional descending As Boolean)

' Dim value As Single