Sort 3 x one dimensional arrays in parallell - vb.net

Question

I have 3 x one dimensional arrays of type integer, each array is the same length (between 5 - 20 million values) and I would like to sort them in parallel (ie keeping the relative position) by the second array, then the third array, then the first array. Does anyone have any ideas on the most efficient way to do this in vb.net?
If it helps, the first array is just a record of the initial position (the three arrays will be re-sorted to this order once various calculations are done). I need to sort them to determine the number of unique combinations of the second and third arrays (a combination is determined by the position in the array - in the example below the combinations are (0-1-4), (1-1-6) etc). Once that is determined I will resort them back based on the first array.
I looked at array.sort but that only covers 2 parallel arrays. I'm a bit wary of putting the values in tuples (or any other format), as it would (I assume - perhaps not) be a big overhead when converting 5 - 20 million records before processing.
For example:
Record Number Array: {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
Link Array: {1, 1, 2, 1, 1, 2, 2, 2, 1, 2}
Line Number Array: {4, 6, 3, 5, 6, 7, 3, 2, 3, 4}
Having sorted / ordered by the second, then third, then first array, the expected output would be:
Record Number (1st Array): {8, 0, 3, 1, 4, 7, 2, 6, 9, 5}
Link Array (2nd Array): {1, 1, 1, 1, 1, 2, 2, 2, 2, 2}
Line Number Array (3rd Array): {3, 4, 5, 6, 6, 2, 3, 3, 4, 7}
Array.sort only allows you to sort 2 arrays in parallel and i'm a little confused by the options available in LinQ.
Does anyone have any suggestions on the best way to solve this problem?
Cheers,

Answer 1

I think you can get a backup of your Link Array. Then sort Link Array with Record Array, then you can sort un-sorted Link Array with Line Number Array. Can you please try it?

Answer 2

You didn't say if you want efficient in terms of time or space, but this takes about 3 seconds to transfer 20 million records from arrays to a list, and then about 30 seconds to do the sort on them, using less than 1GB of RAM. On my computer.
Option Infer On
Module Module1
Class Grouped
Property RecNo As Integer
Property Link As Integer
Property LineNo As Integer
Public Overrides Function ToString() As String
Return String.Format("({0}, {1}, {2})", Me.RecNo, Me.Link, Me.LineNo)
End Function
End Class
Sub Main()
' First try with the test data to show the correct result is obtained
Dim recNos = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
Dim links = {1, 1, 2, 1, 1, 2, 2, 2, 1, 2}
Dim lineNos = {4, 6, 3, 5, 6, 7, 3, 2, 3, 4}
' transfer the arrays to a List
Dim xs As New List(Of Grouped)
xs.Capacity = recNos.Length
For i = 0 To recNos.Length() - 1
xs.Add(New Grouped With {.RecNo = recNos(i), .Link = links(i), .LineNo = lineNos(i)})
Next
' sort the data
Dim ys = xs.OrderBy(Function(x) x.Link).ThenBy(Function(x) x.LineNo).ToList()
Console.WriteLine(String.Join(", ", ys))
' Now try with twenty million records
Dim rand = New Random()
Dim nRecs As Integer = 20000000
recNos = Enumerable.Range(0, nRecs - 1).ToArray()
ReDim links(nRecs - 1)
ReDim lineNos(nRecs - 1)
For i = 0 To nRecs - 1
links(i) = rand.Next(0, 9)
lineNos(i) = rand.Next(1, 9)
Next
Dim sw As New Stopwatch
sw.Start()
xs.Clear()
xs.Capacity = nRecs
For i = 0 To recNos.Length() - 1
xs.Add(New Grouped With {.RecNo = recNos(i), .Link = links(i), .LineNo = lineNos(i)})
Next
sw.Stop()
Console.WriteLine(sw.ElapsedMilliseconds.ToString())
sw.Restart()
ys = xs.OrderBy(Function(x) x.Link).ThenBy(Function(x) x.LineNo).ToList()
sw.Stop()
Console.WriteLine(sw.ElapsedMilliseconds.ToString())
Console.ReadLine()
End Sub
End Module