Help with an array

MarkGT · April 30th, 2008, 01:48 PM

I need to be able to display only the distinct elements of a dynamic array. For example, if the array consists of:

1,2,2,3,4,5,5,5,5,6,7,8,9,9,9,9

then the output in my text box should be:

1,2,3,4,5,6,7,8,9

I can not figure out the code for this. I know how to count the total number of distinct array elements, but I don't know how to display each distinct element. Can anyone help?

gbianchi · April 30th, 2008, 01:57 PM

Hi there.. If you can count them, then you can also show them. Just store the number you are counting, every time you add 1 to your counter and you are done...

HTH

Gonzalo

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MarkGT · April 30th, 2008, 02:24 PM

Hi, thank you for the help. This is the code I have for my counting function:

Code:

Private Function countDistinct(ByVal a() As Integer)
        Dim count, i As Integer
        For i = LBound(a) To (UBound(a) - 1)
            If a(i) = a((i) + 1) Then
                count = count
            Else
                count = count + 1
            End If

        Next
        Return (count + 1)

    End Function

The answer to this seems really simple, but I've been staring at this for hours and can't figure it out. How do I store the numbers I am counting in a variable without actually adding the numbers together?

BrianWren · April 30th, 2008, 03:32 PM

You are only going to return how many distinct values you have. Each time you find a distinct value, you incr. your count.

One way to do this, that is a bit memory wasteful, is to create an integer array that has data about your Array Under Test (AUT).
Each time you hit a distinct element value in the AUT, resize the Data Array (DA) to be large enough to have an element of the same nuber as the value of the element in the AUT, and increment that DA element's value.
So:

Code:

    Dim i as integer
    Dim DA() As Integer
    ReDim DA(0)

    For i = LBound(a) To UBound(a)
        If UBound(DA) < a(i) Then ReDim Preserve DA(0 To a(i))
        DA(a(i)) += 1
    Next i

Having done this, you can travel over DA, and add the index value of any element that is non-zero:

Code:

    For i = LBound(DA) to UBound(DA)

Code:

        If DA(i) > 0 Then Form.TxtBox.Text = "," & i
    Next i

This should get you started. Zero might give you troubles...

You can also use collections to do this. It is slower, but makes more efficient use of memory. Also, this code is basically VB6. There might be better methods in .NETâs array object(s).

gbianchi · April 30th, 2008, 08:17 PM

Do you realize that your code will only work with an ordered array (and in ascending order)?.

HTH

Gonzalo

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MarkGT · April 30th, 2008, 09:46 PM

Yes, I have a function that orders the array in ascending order before I attempt to display the distinct elements. I missed that in the original code I posted.

gbianchi · April 30th, 2008, 10:11 PM

Hey, Hold down your horses.. you are ordering the array before doing this???

Then why not make 2 arrays, 1 ordered and the other ordered too, but with no repetition and at the same time counting the items???

you are doing the work twice...

HTH

Gonzalo

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