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Thread: How to dynamically create ArrayLists (or something similar)?

  1. #1
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    Unhappy How to dynamically create ArrayLists (or something similar)?

    Hi,
    I have an algorithm that using cluster centroids, searches through an array of doubles (see below) putting the values closest to the centroids in repective arrayLists.
    For example (handtyped, not source code, because it works)

    PHP Code:
    double[] array {1,2,3,4,5,6,7,8,9,10}
    double[] centroids {1,4,7
    Using Euclidean distance this creates the following three ArrayLists

    PHP Code:
    list1{1,2}
    list2{3,4,5}
    list3{6,7,8,9,10
    This all works fine, however could someone please help me to dynamically create arrayLists? Right now I'm actually instantiating three of them by hand, but in the working program the number of centroids will be dynamic so the program will need to create as many as required. I was thinking a 2D array, but not really sure if that is the best way to go about this.

    I'm really stuck on this, any help would be hugely appreciated


  2. #2
    Super Moderator Json's Avatar
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    Default Re: How to dynamically create ArrayLists (or something similar)?

    Hello,

    How about using an actual ArrayList rather than an array?

        final List<Double> doubleArray = new ArrayList<Double>();
        doubleArray.add(1.0);
        doubleArray.add(2.0);
        doubleArray.add(3.0);
        doubleArray.add(4.0);
        doubleArray.add(5.0);
        doubleArray.add(6.0);
        doubleArray.add(7.0);
        doubleArray.add(8.0);
        doubleArray.add(9.0);
        doubleArray.add(10.0);

    Something like that, and you can just go on and on and on because arraylists grow while you add things to them

    EnjoY!

    // Json

  3. The Following 2 Users Say Thank You to Json For This Useful Post:

    igniteflow (August 6th, 2009), JavaPF (August 6th, 2009)

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    Default Re: How to dynamically create ArrayLists (or something similar)?

    Thanks for the reply Json.
    I am already using multiple ArrayLists, but my problem is that I want the program to create as many as it requires dynamically. I need to keep the clusters separate, so I don't want to add them all to a single ArrayList, but rather create the same number of ArrayLists as the number of clusters (which is specified by the user). Hope that makes sense.

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    Super Moderator helloworld922's Avatar
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    Default Re: How to dynamically create ArrayLists (or something similar)?

    Create an array list of array lists
    ArrayList<ArrayList<Double>> clusters = new ArrayList<ArrayList<Double>>();

    Then, each time you want a new cluster do:
    ArrayList<Double> set = new ArrayList<Double>();
    // add stuff to set
    set.add(5);
    ...
    clusters.add(set);

  6. The Following 2 Users Say Thank You to helloworld922 For This Useful Post:

    igniteflow (August 6th, 2009), JavaPF (August 6th, 2009)

  7. #5
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    Default Re: How to dynamically create ArrayLists (or something similar)?

    Awesome, thanks helloworld922!!

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