How to initialize a multidimensional array on the go in java

Question

I have a multidimensional array where the second dimension is not always the same length.

Is it possible to initialize an array where you first create the first part like this

I am using this array to define the length of each row in the matrix.

int[] config = {4,4,4,3,2,4};

boolean[][] array = new boolean[config.lenght][];

and then after loop over the array and create the subarrays with the desired length?

for(int i = 0; i<config.length; i++)
    boolean[i][] = new boolean[config[i]];

PS: I will not use ArrayList

do you need to make store values in the array before you define the length of the 2nd dimension? — Luke
– Luke, Commented Oct 18, 2020 at 22:26
You mean a jagged array? You can initialize the size of the 2nd dimension separate from the first. — Omar Abdel Bari
– Omar Abdel Bari, Commented Oct 18, 2020 at 22:26
The word jagged array helps me i think, but the link didn't answer :) — mama
– mama, Commented Oct 18, 2020 at 22:30

Oleg Cherednik · Accepted Answer · 2020-10-18 22:31:09Z

1

public static int[][] generate(int[] config) {
    int[][] arr = new int[config.length][];
    Random random = new Random();

    for (int row = 0; row < arr.length; row++) {
        arr[row] = new int[config[row]];

        for (int col = 0; col < arr[row].length; col++)
            arr[row][col] = random.nextInt(100);
    }

    return arr;
}

Output:

[
  [97, 80, 78, 88],
  [31, 97, 34, 39],
  [67, 92, 89, 0],
  [29, 96, 72],
  [68, 77],
  [7, 65, 68, 51]
]

answered Oct 18, 2020 at 22:31

Oleg Cherednik

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2 Comments

mama Over a year ago

This is exactly what I wanted to do. :-)

mama Over a year ago

I am too tired. and I did alot of small mistakes. Thank you, this helped me alot.

Atakan Kocaayan · Accepted Answer · 2020-10-18 22:33:32Z

0

I do not fully understand the question, but I have a suggestion for a solution like this.

            int[] config = {4,4,4,3,2,4};
            int[][] array = new int[config.length][config.length];
            for(int i = 0 ; i<config.length ; i++){
                array[i][0] = config[i];
            }

array output:

answered Oct 18, 2020 at 22:33

Atakan Kocaayan

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Comments

WJS · Accepted Answer · 2020-10-18 22:37:00Z

0

You can assign any single D array to a 2D array of the same type.


int[] s = {1,2,3,4,5,6};

int[][] twoD = new int[s.length][];

for (int i = 0; i < v.length; i++) {
   twoD[i] = new int[]{s[i]}; // new array of one element of the `s` array
}

for ( int[] s : twoD) {
  System.out.println(s);
}

Prints

[1]
[2]
[3]
[4]
[5]
[6]

or

System.out.println(Arrays.deepToString(twoD));

Prints

[[1], [2], [3], [4], [5], [6]]

edited Oct 18, 2020 at 22:37

answered Oct 18, 2020 at 22:30

WJS

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2 Comments

mama Over a year ago

I will try to clarify my question. I am using a normal array to initialize the 2d array

WJS Over a year ago

OK. This uses the existing array to initialize your 2D array.

Eritrean · Accepted Answer · 2020-10-18 22:43:26Z

0

You can also use streams:

int[] config = {4,4,4,3,2,4};
boolean[][] myArr = Arrays.stream(config).mapToObj(i -> new boolean[i]).toArray(boolean[][]::new);
    
for(boolean[] b : myArr){
    System.out.println(Arrays.toString(b));
}

answered Oct 18, 2020 at 22:43

Eritrean

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