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vb.net delete random from ArrayList

Posted on 2013-10-31
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Last Modified: 2013-10-31
Hello,
I have an ArrayList called "lastnames" with 20 items.
I would like to know whats the easiest way to remove random items from it leaving it with only 5 records.. how can I do this?
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Question by:XK8ER
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5 Comments
 
LVL 2

Expert Comment

by:BakuRetsu_X
ID: 39615352
Create a random number generator object up to the size of your matrix.
Once you grab a number, take that as your array index to remove from the array.
Are you looking for code example?

Search vb.net random number generator on google.
Then search remove from array list vb.net.
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LVL 1

Author Comment

by:XK8ER
ID: 39615359
yeah I tried that but for example I do

myAL.RemoveAt(5)
myAL.RemoveAt(8)
myAL.RemoveAt(12)

at this point i have only 17 items in the arraylist so when I do

myAL.RemoveAt(19)

it crashes
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LVL 75

Assisted Solution

by:käµfm³d 👽
käµfm³d   👽 earned 1000 total points
ID: 39615682
Make sure the next random number you generate is never larger than the maximum index of your collection.

e.g.

Dim rand As New Random()
Dim myAL As New ArrayList() = SomeInitialization()
Dim toRemove As Integer = rand.Next(0, myAL.Count)

myAL.RemoveAt(toRemove)

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LVL 86

Accepted Solution

by:
Mike Tomlinson earned 1000 total points
ID: 39615786
Another quick example:
        Dim R As New Random
        While lastnames.Count > 5
            lastnames.RemoveAt(R.Next(lastnames.Count))
        End While

Open in new window

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LVL 2

Expert Comment

by:BakuRetsu_X
ID: 39615795
Remember.  The array is constantly shrinking also. So each time you want the random number to be within the length of it.
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