Detecting / Counting Duplicate Items in a ListBox

This code sample shows how to detect and count the duplicate entries in a ListBox, it could also be adapted to be used with a ComboBox control.

The code makes use of the SendMessage API along with the ListBox LB_FINDSTRINGEXACT windows message to detect duplicate items. If you were changing the code to work with a combo, you would use the CB_FINDSTRINGEXACT message instead.



private Declare Function SendMessage Lib "user32" Alias "SendMessageA" _
        (byval hwnd as Long, byval wMsg as Long, _
        byval wParam as Long, lParam as Any) as Long

private Const LB_FINDSTRINGEXACT = &H1A2

private Sub Command1_Click()
    Dim iIndex as Long
    Dim iMatch as Long
    Dim iCopies as Long
    Dim iHighest as Long
    Dim aCommon() as Long
    Dim sString as string
    Dim bSkip as Boolean

    for iIndex = 0 to List1.ListCount - 1
        iCopies = 0
        iMatch = -1
        bSkip = false
        'Skip this one if it's the same as the last Item Checked
        If iIndex then
            bSkip = (List1.List(iIndex) = List1.List(iIndex - 1))
        End If

        'Skip this one if there's a previous instance of it in the List
        If Not bSkip then
            bSkip = (SendMessage(List1.hwnd, LB_FINDSTRINGEXACT, -1, _
                    byval List1.List(iIndex)) < iIndex)
        End If
        'While there are other Instances in the List..
        While iMatch <> iIndex And Not bSkip
            'Increment the No of Copies Found of this Item
            iCopies = iCopies + 1
            'Find the next Copy..
            iMatch = SendMessage(List1.hwnd, LB_FINDSTRINGEXACT, _
                 IIf(iMatch < 0, iIndex, iMatch), _
                 byval List1.List(iIndex))
        Wend
        'If there were more than 1 Copies
        If iCopies > 1 And Not bSkip then
       'If the No. of Copies is Greater or the Same as the Highest so far..
            If iCopies >= iHighest then
                If iCopies > iHighest then
                    'new Highest Copies
                    ReDim aCommon(0)
                else
                'Another Item with the same highest amount of Copies
                    ReDim Preserve aCommon(UBound(aCommon) + 1)
                End If
                'Store this Index
                aCommon(UBound(aCommon)) = iIndex
                'Remember the Highest No. of Copies
                iHighest = iCopies
            End If
        End If
    next
    If iHighest then
        'If Copies were Found..
        for iIndex = 0 to UBound(aCommon)
            sString = sString & ", " & List1.List(aCommon(iIndex))
        next
        MsgBox "Most Repeated Item(s): " & vbCrLf & mid$(sString, 3) & _
                vbCrLf & vbCrLf & "Repeated " & iHighest & " Times.", _
                vbInformation + vbOKOnly, "Repeats"
    else
        'No Copies Found..
        MsgBox "No Items were Repeated", vbInformation + vbOKOnly, _
          "No Repeats"
    End If
End Sub
'
'

Download Zipped Project file (5k)

screen-shot



Comments

  • There are no comments yet. Be the first to comment!

Leave a Comment
  • Your email address will not be published. All fields are required.

Top White Papers and Webcasts

  • Live Event Date: December 11, 2014 @ 1:00 p.m. ET / 10:00 a.m. PT Market pressures to move more quickly and develop innovative applications are forcing organizations to rethink how they develop and release applications. The combination of public clouds and physical back-end infrastructures are a means to get applications out faster. However, these hybrid solutions complicate DevOps adoption, with application delivery pipelines that span across complex hybrid cloud and non-cloud environments. Check out this …

  • VMware vCloud® Government Service provided by Carpathia® is an enterprise-class hybrid cloud service that delivers the tried and tested VMware capabilities widely used by government organizations today, with the added security and compliance assurance of FedRAMP authorization. The hybrid cloud is becoming more and more prevalent – in fact, nearly three-fourths of large enterprises expect to have hybrid deployments by 2015, according to a recent Gartner analyst report. Learn about the benefits of …

Most Popular Programming Stories

More for Developers

RSS Feeds