Collect Numbers from a 2D Array

Question

I would like to wirte a method called collectNums which is supposed to collect all the elements of the type Number from a 2D Object Array. Then I would like to collect all of the elements of type Number in a List and return it.

Here's my code:

public static List<Number> collectNums(Object nrAry[][])
{
    List<Number> numbers = new ArrayList<Number>();
    for(int i = 0; i < nrAry.length; i++) 
    {
        for(int j = 0; j < nrAry[i].length; j++)
        {
            if (nrAry[i][j] instanceof Number) 
            {
                numbers.add(j);
                numbers.add(i);
            }
        }
    }
    return numbers;
}

Please let me know if I have not made myself clear. Thanks everyone!

This doesn't look like best practice to me. I think it would be better to take an array of `Number`. — Tim Biegeleisen, Jan 18 '18 at 10:23
Thank you for your comment. It is a task set by my lecturer so I saldy cannot change too much of the actual task. — John_Doe, Jan 18 '18 at 10:26
This question converts 2d array to list. Please, Look this solution : https://stackoverflow.com/questions/11447780/convert-two-dimensional-array-to-list-in-java — ramazankul, Jan 18 '18 at 10:36

score 3 · Accepted Answer · answered Jan 18 '18 at 10:22

3

You are collecting the indices of the array instead of the values stored in the array.

public static List<Number> collectNums(Object nrAry[][])
{
   List<Number> numbers = new ArrayList<Number>();
   for(int i=0;i < nrAry.length; i++)  {
       for(int j=0;j < nrAry[i].length; j++) {
            if (nrAry[i][j] instanceof Number)  {
                numbers.add((Number)nrAry[i][j]);
            }
        }
    }
    return numbers;
}

answered Jan 18 '18 at 10:22

Eran

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Oh thank you, I am still having trouble with arrays. I might need to read up on it more. – John_Doe Jan 18 '18 at 10:27

score 0 · Answer 2 · answered Jan 18 '18 at 10:58

In Java 8 it can be simpler:

public static List<Number> collectNums(Object nrAry[][]) {
        return Arrays.stream(nrAry)
                .flatMap(Arrays::stream)
                .filter(x -> x instanceof Number)
                .map(x -> (Number) x)
                .collect(Collectors.toList());
    }

Collect Numbers from a 2D Array

2 Answers2