2D array representation using Arraylist

Question

I would like to implement a 2D representation of data where each of the row represents features which are in gaussian distribution. I did the following:

     public ArrayList<ArrayList<Double>> getFeature( BufferedReader buffer1)

  {   ArrayList<Double> arrList1 = new ArrayList<Double>();
    ArrayList<ArrayList<Double>> arrList2 = new ArrayList<ArrayList<Double>>();
    String[] strArr = getWords(buff1); 
    for(int j=0 ; j< strArr.length; j++){
    for(int i =0 ;i < 50 ; i++){
        arrList1.add(rand.nextGaussian());
    }
    arrList2.add(arrList1);
    }
    System.out.println("size of arrList2:"+ arrList2.size());       
    System.out.println(arrList2.toArray()[0]);
    System.out.println(arrList2.toArray()[1]);
    return arrList2;
}

When i compile and wants to get the value of each of the row, i get weired output. Can anybody tell me what can be the reason ?

The expected output is:

  System.out.println(arrList2.toArray()[0]);

 [0.08,1.1 .............,0.98]

An array of dimension 50 filled with the value as above.

The following is the weired output. It was too big

[0.46462618324716254, -0.7461971643031985, 0.11198107553318244, -0.5445576195764561, -0.09170153174710902, 1.0599085675813804, -0.5121868425685772, 0.6578194527724543, 0.07180836719554716, -0.8711795090831688, -1.1685999674955914, -0.8467566589850426, -0.9464559617558149, -0.25455126102711567, 0.6880497852836619, 0.05802417861623583, 0.7605219159096197, 0.5573206594413265, -0.6464485036951102, 0.9928577372480463, 0.769468353755745, -1.0349221359588956, 1.7475686681406222, 0.7286721770852165, 1.1938115793074722, 0.05051321258899094, -1.5274223735062666, -0.10652710930319426, -2.1566969444968622, 1.4572264331572156, -0.07630289414615696, 0.2776127747056551, -0.3009457462994894, 0.9554273666202241, -2.1190393953455047, 0.4580572585843065, -0.6413109094169921, -0.4978755907488374, 0.353842909950826, -1.257672808328245, -0.3236234929243931, -0.8899339209743886, 0.347442395255124, -0.48611580230648704, 1.219007569267497, -1.1789975566918134, -0.01825901882420379, -1.6486718275722763, -0.3819 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Answer 1

You need to reinitialize your arrList1 at every iteration of the outer loop:

for(int j = 0; j < strArr.length; j++){
    arrList1 = new ArrayList<Double>();
    for(int i = 0; i < 50; i++){
       arrList1.add(rand.nextGaussian());
    }
    arrList2.add(arrList1);
}

otherwise you keep adding to the same ArrayList , which is the reason for the huge output you are getting.

Answer 2

You're using the same instance for arrList1 throughout.

Try:

for(int j=0 ; j< strArr.length; j++){
    arrList1 = new ArrayList<Double>();
    for(int i =0 ;i < 50 ; i++){
        arrList1.add(rand.nextGaussian());
    }
    arrList2.add(arrList1);
}