How to create an array from a pre-existing array?

Question

New to java and am trying to create a program/method that will take an int array, and return another int array but it replaces the values of the indexes with the value of the elements. (Example {2,1,3} will return {0,0,1,2,2,2}

public static void main(String[] args) {

    int[] pracArray = {2, 1, 3};

    int sum = 0;

    for (int i = 0; i < pracArray.length; i++)
    {
        sum = sum + pracArray[i];
    }

    System.out.println("Amount of array indexes: " + sum);

    int[] newArray = new int[sum];

    System.out.println(Arrays.toString(pracArray));

    for (int i = 0; i < pracArray.length; i++)
    {

        for (int j = 0; j < pracArray[i]; j++)
        {
            newArray[j] = i;
        }
    }
    System.out.println(Arrays.toString(newArray));
}

}

Currently I am getting [2,2,2,0,0,0]. I have tried changing the how many times each for loop iterates with no avail. I have also tried to make the elements of newArray equal to a counter ( int count = 0; and having count++ in the for loop) since the values of the new array will always be 0 - however many runs.

Your second loop should definitely not start at j=0 for every value in the original array. Your code pretty much works except that j should start at "however many elements we already wrote before the current inner loop iteration", — Mike 'Pomax' Kamermans
– Mike 'Pomax' Kamermans, Commented Mar 7, 2020 at 1:00
@Jason , yea my output has to be an array, but if you could do it without it being an array I would still like to see it and appreciate the help — tomatofighter
– tomatofighter, Commented Mar 7, 2020 at 1:06
@Mike'Pomax'Kamermans what would be the best way to go about that? I originally tried setting j to a temp variable and also counter of each run but neither would give an output that would help fix my problem — tomatofighter
– tomatofighter, Commented Mar 7, 2020 at 1:15
what do you mean by "it replaces the values of the indexes with the value of the elements. (Example {2,1,3} will return {0,0,1,2,2,2}" i didn't get it — Abhinav Chauhan
– Abhinav Chauhan, Commented Mar 7, 2020 at 3:31

Surronie · Accepted Answer · 2020-03-07 01:38:28Z

1

Given the length of your array is 3, your outer 'i' loop is iterating through the values 0,1,2. That means your inner 'j' loop never writes to index 3,4,5 (hence why they are 0 in the output), and why the first 3 indexes are set to '2' (2 is the last indexed processed in the 'i' loop). Try this instead...

int h = 0;

for (int i = 0; i < pracArray.length; i++)
{
    for (int j = 0; j < pracArray[i]; j++)
    {
        newArray[h] = i;

        h++;
    }
}

edited Mar 7, 2020 at 1:38

answered Mar 7, 2020 at 1:17

Surronie

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