:
: Hello all,
:
: I have a string array with duplicate elements. I need to create a new
: string array containing only the unique elements. Is there an easy way
: to do this? I have tried looping through each element but I am having
: issues using redim to adjust the new array. Any help or example code
: would be greatly appreciated. thanks!
Arrays are fixed length and generally are best used when you know in advance
(or can easily calculate) how large it needs to be and if you are not going
to be changing the size of the array frequently (if at all).
For your purposes here, try using the ArrayList object instead (see
namespace System.Collections). You can dynamically add strings (or any
object for that matter) to the array without having to concern yourself with
the hassles and performance issues associated with redimensioning regular
arrays.
Here is a quick example (VB.NET 2.0):
'******************************************************
Option Strict
Imports Microsoft.VisualBasic
Imports System
Imports System.Collections
Public Module MyModule
Public Sub Main
Dim S1(10) As String
Dim S2() As String
Dim AR As New ArrayList
Dim ndx As Integer
'Create a string array with duplicate entries for entries
'"Item 1", "Item 2" and "Item 6"
s1(0) = "Item 1"
s1(1) = "Item 3"
s1(2) = "Item 2"
s1(3) = "Item 4"
s1(4) = "Item 1"
s1(5) = "Item 2"
s1(6) = "Item 6"
s1(7) = "Item 5"
s1(8) = "Item 6"
s1(9) = "Item 2"
s1(10) = "Item 1"
'Display the contents of S1
DumpArray(S1, "Contents of S1()")
'Load only unique values to an array list object
For ndx = 0 To 10
If Not Ar.Contains(S1(ndx)) Then
Ar.Add(S1(ndx))
End If
Next
'Go ahead and sort this array list just for grins and giggles
Ar.Sort
'Turn this back into an array
ReDim S2(Ar.Count - 1)
For ndx = 0 To Ar.Count - 1
S2(ndx) = CType(Ar.Item(ndx), String)
Next
'Now let's print out the contents of array S2
DumpArray(S2, "Contents of S2()")
End Sub
Private Sub DumpArray(S() As String, msg As String)
Dim ndx As Integer
Console.WriteLine(msg)
Console.WriteLine("--------------------------------------")
For ndx = 0 to UBound(S)
Console.WriteLine(S(ndx))
Next
Console.WriteLine
End Sub
End Module
'******************************************************
This will produce the following output:
Contents of S1()
--------------------------------------
Item 1
Item 3
Item 2
Item 4
Item 1
Item 2
Item 6
Item 5
Item 6
Item 2
Item 1
Contents of S2()
--------------------------------------
Item 1
Item 2
Item 3
Item 4
Item 5
Item 6
Please notice a few things about this code.
1 - I did not define the size of S2 at first since I didn't know going in
what size it would be when the process was complete
2 - I didn't assign an initial value to the ArrayList object either. I just
added objects as needed and it handled all that work
3 - I was able to easily avoid duplicate entries by using the .Contains
method of the ArrayList.
4 - The original array was not sorted but the final array was. All I needed
was a simple one-line statement to achieve this: AR.Sort
5 - The ArrayList stored everything as an Object. When I get those objects
back out of the ArrayList, I have to recast them as String objects (using
the CType keyword)
6 - I was able to correctly size array S2 when I finally reached that point
by referencing the .Count property of the ArrayList. There was no need for
me to track that myself.
HTH
Ralf
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