How to convert 2-dimensional double array from 2-dimensional Integer array in Java

Question

I am trying to create a utility function to create a 2-dimensional array of doubles out of a 2-dimensional array of Integers (which is created from deeplearning4j's KerasTokenizer's textsToSequences(String[] texts) method). I created the method below but keep getting NullPointerExceptions at line 111 (doubles[i][j] = list.get(j);). How can I change my method or create a new one to fix this problem?

public static double[][] integerToDoubleArray(Integer[][] integers) {
        double[][] doubles = new double[integers.length][];
        for (int i = 0; i < integers.length; i++) {
            List<Integer> list = Arrays.asList(integers[i]);
            for (int j = 0; j < list.size(); j++) {
                doubles[i][j] = list.get(j);
            }
        }
        return doubles;
    }

I call it using the following method with the following API: https://deeplearning4j.org/api/latest/org/deeplearning4j/nn/modelimport/keras/preprocessing/text/KerasTokenizer.html#textsToSequences-java.lang.String:A-

private static double[][] encodeSequences(KerasTokenizer tokenizer, int length, ArrayList<String> sentences) {
        return integerToDoubleArray(tokenizer.textsToSequences(arraylistToArray(sentences)));
    }

@luk2302 The issue is actually that each element of `doubles` was not initialized. — Unmitigated, Jul 08 '20 at 19:13

Unmitigated · Accepted Answer · 2020-07-08T19:15:20.067

You did not specify the second dimension of doubles (which is an array of double arrays), nor did you initialize each element of it, so you are getting this exception. Just initialize each row to a new double array with the length of the integer array at that index.

public static double[][] integerToDoubleArray(Integer[][] integers) {
    double[][] doubles = new double[integers.length][];
    for (int i = 0; i < integers.length; i++) {
        doubles[i] = new double[integers[i].length];
        List<Integer> list = Arrays.asList(integers[i]);
        System.out.println(list);
        for (int j = 0; j < list.size(); j++) {
            doubles[i][j] = list.get(j);
        }
    }
    return doubles;
}

It should be noted that you do not need to convert each row of the two dimensional Integer array to a List, as you can simply use integers[i][j] to access the element at row i and column j. Demo

public static double[][] integerToDoubleArray(Integer[][] integers) {
    double[][] doubles = new double[integers.length][];
    for (int i = 0; i < integers.length; i++) {
        doubles[i] = new double[integers[i].length];
        for (int j = 0; j < integers[i].length; j++) {
            doubles[i][j] = integers[i][j];
        }
    }
    return doubles;
}

score 1 · Answer 2 · answered Jul 08 '20 at 19:18

This could solve your problem. I dont see any reason to use ArrayList during convertion.

public static double[][] integerToDoubleArray(Integer[][] integers) {
        
        //TODO: return empty double[][] array if integers 2-D array is empty
        
        double[][] doubles = new double[integers.length][integers[0].length];
        for (int i = 0; i < integers.length; i++) {
            for (int j = 0; j < integers[0].length; j++) {
                doubles[i][j] = integers[i][j];

            }
        }
        return doubles;
    }

How to convert 2-dimensional double array from 2-dimensional Integer array in Java

2 Answers2