Sort and Search arrays using IComparable

A

alreadyused

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Jan 13, 2006
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I am looking for feedback on this code/idea.

What I want to do is load tables and throw away tables as needed. Some tables I will want to keep loaded for a while.

For example, at runtime I find that i need a table so I try to get it from an array.
If it's there, get it, if not load it (this isn't shown below; I add 5 dummy tables for testing)
When I'm done with it (whenever that may be) I remove it.

I started with the code basically mimicking PlausiblyDamp's suggestion in this post:
http://www.xtremedotnettalk.com/showthread.php?t=83236
It sorted fine, but when I went to do a search on the array, it crashed because I was passing the table name and not a "TableClass", and it was trying to cast a string to type TableClass.

Again starting from one of PD's suggestions from here:
http://www.xtremedotnettalk.com/showthread.php?t=82561
I tested the object passed in to make sure it has a toString function.
Sooooo, here is a very basic test for what I'm wanting to do:

Visual Basic: 
Module modMain
  Sub Main()

    Dim oTest As New FindTest
    Dim name As String
    For i As Integer = 1 To 5
      name = "a" & i.ToString
      oTest.addTable(name)
    Next

    Dim tbl As TableClass = oTest.findTable("a1")
    MessageBox.Show(tbl.getName)

    oTest.removeTable("a3")

  End Sub
End Module


Public Class FindTest
  Private tbl() As TableClass

  Public Sub addTable(ByVal name As String)
    
    Dim xd As New Xml.XmlDocument
    Dim o As New TableClass(name, xd)
    Dim i As Integer

    If Me.tbl Is Nothing Then
      i = 0
    Else
      i = Me.tbl.GetUpperBound(0) + 1
    End If

    ReDim Preserve Me.tbl(i)
    Me.tbl(i) = o
    Me.tbl.Sort(Me.tbl)
  End Sub

  Public Function findTable(ByVal name As String) As TableClass
    Dim i As Integer = Me.tbl.BinarySearch(Me.tbl, name)
    Return tbl(i)
  End Function

  Public Function removeTable(ByVal name As String) As TableClass
    Dim t1() As TableClass
    Dim count As Integer = -1

    Dim i As Integer = Me.tbl.BinarySearch(Me.tbl, name)

    If i >= 0 Then
      For j As Integer = 0 To Me.tbl.Length - 1
        If j <> i Then
          count += 1
          ReDim Preserve t1(count)
          t1(count) = Me.tbl(j)
        End If
      Next
    End If

    Me.tbl = t1

  End Function
End Class


Public Class TableClass
  Implements IComparable

  Private name As String
  Private table As Xml.XmlDocument

  Public Sub New(ByVal name As String, ByVal table As Xml.XmlDocument)
    Me.name = name
    Me.table = table
  End Sub
  Public Function getName() As String
    Return Me.name
  End Function
  Public Function getTable() As Xml.XmlDocument
    Return Me.table
  End Function
  Public Overrides Function toString() As String
    Return Me.name
  End Function

  Public Function CompareTo(ByVal obj As Object) As Integer Implements System.IComparable.CompareTo
    Try
      Dim name As String = obj.ToString
    Catch ex As Exception
      Throw New InvalidOperationException("Objects must have toString function for comparison.")
    End Try

    If String.Compare(Me.name, name) < 0 Then Return -1
    If String.Compare(Me.name, name) > 0 Then Return 1
    Return 0

  End Function
End Class

This code compiles and runs fine; does what I want it to do.

What I'm curious about is:
  1. Does this make sense to be doing this?
  2. Is there an easier or more efficient way to remove an item from an array?
  3. Am I doing the Compare correctly?
  4. Does anyone see any other errors or things I should improve on?

Thanks in advance!
 
Consider a Dictionary

Personally I would suggest using a Dictionary or Hashtable to associate each TableClass with its name. Unless you have a need to sort the tables besides faster access (which the Dictionary provides) this would definitely be preferable. It would also take care of resizing the collection as tables are inserted or removed, and more efficiently than your code appears to do.

On an unrelated note, all objects expose a ToString method so the try/catch block would be unnecessary.

Good luck :)
 
Re: Consider a Dictionary

awesome on the try/catch! figures, i looked over this and was thinking, ok, i'm not doing anything stupid... ooops

I don't need the tables sorted other than for fetching or removing.

I'll check out the dictionary, thanks!
 
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