Copyright © 2004-2005
| IComparer: Compare |
Compares two elements and returns their relationship.
Public Function Compare( ByRef x As Variant, ByRef y As Variant ) As Long
Comparison guide:
x is the same value as y returns a 0.
x is less than the value y returns a negative value (-1).
x is greater than the value y returns a positive value (1).
To begin you will need the following items in a new Standard EXE project.
1. A Reference to the VBCorLib library. This should be named VB.EXT: VBCorLib
2. A Module file with Main set as your startup choice.
3. A Class file that will implement the IComparer interface.
Once the project is set up we can write our compare logic in the class. The followingis the entire contents of the Class. Rename the class to OddEvenComparer and putthe following code in its code window.
' We want to sort our numbers by grouping them in odd and even'' groups. We want all odd numbers to be first in the list and'' all even numbers to be last. Within each odd and even group'' we want those number to be sorted in ascending order in that group.'''' Our comparer will compare on two levels. The first level'' is to compare whether or not the two values are odd or even.'' If they are both odd or both even, then they belong in the'' same group, so we just compare them as normal to keep them'' sorted within their group. If one is odd and the other is even,'' then we want all odd numbers to be first in the sorted list.'' This means they are a lesser value than even numbers, even if'' the actual value is greater.'''' Example: 7 is less than 2 because 7 is odd.''Option Explicit'' Implement the IComparer interface to allow for custom'' comparisons to take place when sorting an array.Implements IComparer'' The IComparer interface implementation.'' The return value indicates if x is less than, equal to, or'' greater than y. Any method can be used to compare x to y,'' as long as it is consistant.'''' x < y should return a negative value'' x = y should return zero'' x > y should return a positive valuePrivate Function IComparer_Compare(x As Variant, y As Variant) As Long '' Check to see if x and y are both odd or both even. If (x And 1) = (y And 1) Then '' x and y are the same (odd or even), so we will '' just use the default comparer object for them. IComparer_Compare = Comparer.Default.Compare(x, y) ElseIf x And 1 Then '' if x is odd then we must indicate that x is less '' than y by returning a negative value. IComparer_Compare = -1 Else '' x is even, therefore y is odd. x is then a '' greater value and we indicate that by return '' a positive value. IComparer_Compare = 1 End IfEnd Function
Now that the OddEvenComparer class is written, we can focuse onthe Main method. In the Module code window copy the following.
Option ExplicitPrivate Sub Main() Dim ints() As Long Dim i As Long '' Create an array using all digits from 0-9. ints = cArray.NewArray(ciLong, 6, 4, 2, 8, 7, 1, 9, 0, 5, 3) '' sort the array using our custom IComparer object. cArray.Sort ints, New OddEvenComparer '' Display the sorted array. For i = 0 To 9 '' We use the formatting capabilities of the Console class '' to allow for easy value replacement within the output string. Console.WriteLine "ints({0}) = {1}", i, ints(i) Next i '' Wait for user. Console.WriteLine "Press Enter" Console.ReadLineEnd Sub'' This code will produce the following output.'''' ints(0) = 1'' ints(1) = 3'' ints(2) = 5'' ints(3) = 7'' ints(4) = 9'' ints(5) = 0'' ints(6) = 2'' ints(7) = 4'' ints(8) = 6'' ints(9) = 8'' Press EnterAs you can see, using our custom comparer enables us to sort an array usingwhat ever logic we need. This allows the framework to be extended to the user'sneeds as they are.
Project VBCorLib Overview Class IComparer Overview IComparer Properties IComparer Methods