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How to overwrte an arraylist location

How can I overwrite an arraylist location?

Example
4000
0
4001

I need to overwrite the value 0 which in in my arraylist with the value 4000

0
cmdolcet
Asked:
cmdolcet
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1 Solution
 
Jorge PaulinoIT Pro/DeveloperCommented:
Can you simply remove it ?
        Dim arr As New ArrayList
        arr.Add(4000)
        arr.Add(0)
        arr.Add(4001)
 
        ' Removes the 0
        arr.Remove(0)

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cmdolcetAuthor Commented:
but I don't want to remove it i want to update it with the previous arraylist value
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Mike TomlinsonMiddle School Assistant TeacherCommented:
Just access it by Index:

    arr(1) = 4000 ' replace the second element with 4000
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Jorge PaulinoIT Pro/DeveloperCommented:
Then follow the Idle_Mind suggestion ... I thought you wanted to delete the wrong entry.
If you don't know the index of the 0 (zero) you can use:

arr(arr.IndexOf(0)) = New Value
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cmdolcetAuthor Commented:
I keep getting a break error after the second loop through
I have _Arraylist_1Inch which has 24 spot in the arraylist. Every 2 index position I have written a 0 integer value what this loop should do is loop through the       _Arraylist_1Inch       and replace the 0 value with the goodpre_intarrayindex value

However its breaking


    For Each intarrayindex In _Arraylist_1Inch
                    If intarrayindex = 0 Then
                        _Arraylist_1Inch(intarrayindex) = pre_intarrayindex
                    Else
                        pre_intarrayindex = 0
                        pre_intarrayindex = intarrayindex
                    End If
                Next
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Jorge PaulinoIT Pro/DeveloperCommented:

intarrayindex gives you the value in the array and you're trying to use as the index of the  array  _Arraylist_1In in here
  _Arraylist_1Inch(intarrayindex)
I don't know what you want to replace with but you can do something like this (and change the 123 with your value)

        Dim pos As Integer
        While True
            pos = _Arraylist_1Inch.IndexOf(0)
            If pos = -1 Then Exit While
            _Arraylist_1Inch(pos) = 123
        End While

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Mike TomlinsonMiddle School Assistant TeacherCommented:
I think you want?

        For intarrayindex As Integer = 0 To _Arraylist_1Inch.Count - 1
            If _Arraylist_1Inch(intarrayindex) = 0 Then
                _Arraylist_1Inch(intarrayindex) = pre_intarrayindex
            End If
        Next
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Jorge PaulinoIT Pro/DeveloperCommented:
Nice solution Idle_Mind, the only problem is that loops in all the arraylist.
But, could be not a problem :)
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Mike TomlinsonMiddle School Assistant TeacherCommented:
Yeah...it's not very clear how it's supposed to work...

If you LITERALLY want to visit "Every 2 index position" then use the Step keyword on the end of the For loop:

        For intarrayindex As Integer = 0 To _Arraylist_1Inch.Count - 1 Step 2
            If _Arraylist_1Inch(intarrayindex) = 0 Then
                _Arraylist_1Inch(intarrayindex) = pre_intarrayindex
            End If
        Next

You would just need to start at 0 or 1 depending on which slot was the first one you needed.
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Mike TomlinsonMiddle School Assistant TeacherCommented:
@jpaulino: With regard to this part of your comment:

    "...the only problem is that loops in all the arraylist."

I do hope you realize that your code is ALSO visiting all slots in the ArrayList.  Internally, the IndexOf() method is doing exactly what I have done: loop thru iteratively, inorder, until it finds a match.

In fact, your algorithm is potentially ALOT worse because EACH call to IndexOf() is starting from the BEGINNING of the ArrayList and looking for a match.  So you will be iterating over some nodes multiple times!  In fact, if the whole thing was full of zeroes then you would be doing multiple passes with a total of (1 + 2 + 3 + 4 + ... + n) checks instead of a just 1 pass with n checks.   =\

You would need to use the IndexOf() overload that accepts a "starting position" to overcome this:

        Dim pos As Integer, startIndex = 0
        While True
            pos = _Arraylist_1Inch.IndexOf(0, startIndex)
            If pos = -1 Then Exit While
            _Arraylist_1Inch(pos) = 123
            startIndex = pos + 1
        End While

~IM   =)
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Jorge PaulinoIT Pro/DeveloperCommented:
Strange I have made a few tests and the time from your method and my (including you change) is very close. Sometimes my runs fasts, sometimes your code runs faster.
But that the startIndex it's needed or else it will increase ALLOT the cycle time
Loved you sign ~IM :)
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Jorge PaulinoIT Pro/DeveloperCommented:
Typo ... Should be:

Loved your sign ~IM :)
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Mike TomlinsonMiddle School Assistant TeacherCommented:
Lol...and of course, if the size of the list is small, then the milliseconds saved doesn't really matter!   =O


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Jorge PaulinoIT Pro/DeveloperCommented:
I have tested with 20000 records!
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