Iterate over shallow copy of nested array in Javascript

Question

I have a nested array:

let array = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];

I need to iterate over the first and second element of every nested array and update the changes on the original array. How do I achieve this? I have tried many options but the results don't update the original array. For example:

let arrayCop = [];
for (let i = 0; i <= 1; i++) {
   for (let j = 0; j <= 1; j++) {
      arrayCop.push(array[i][j]);
   }
}

arrayCop.forEach(...);

Thanks.

This is my full code, I'm trying to build a legal sudoku generator:

let sudoku = [];

function populateSudoku() {
    let array = [];
    while (array.length <= 8) {
        let randomNum = Math.floor(Math.random() * 9 + 1);
        array.push(randomNum);
        if (array.indexOf(randomNum) < array.lastIndexOf(randomNum)) {
            array.pop()
        }
    }
    return array;
}

while (sudoku.length <= 8) {
    sudoku.push(populateSudoku());
}

for (let i = 0; i < sudoku.length; i++) {
    for (let j = 0; j < sudoku.length; j++) {
        sudoku[i].forEach(element => {
            if (sudoku[i].indexOf(element) === sudoku[j].indexOf(element) &&
                (i !== j)) {
                sudoku[j][sudoku[i].indexOf(element)] = 0;
            }
        })
    }
}

let array = [];

for (let i = 0; i <= 2; i++) {
    for (let j = 0; j <= 2; j++) {
        array.push(sudoku[i][j]);
    }
}

array[3] = 452345;

console.log(sudoku);

**

# I did it! #

**

let array = [[1, 2, 3], [7, 4, 1], [2, 4, 3]];

// checks for duplicates just in first and second item of every file
for (let i = 0; i <= 1; i++) {
    for (let j = 0; j <= 2; j++) {
        array[i].forEach((element, index) => {
            if ((i !== j) && index <= 1 &&
            (array[j].indexOf(element) >= 0 && array[j].indexOf(element) <= 1)) {
                array[i][index] = 'x';
            }
        })
    }
}

console.log(array);

arrayCop.forEach(...); yes, where ... is your attempt to do so — Jaromanda X
– Jaromanda X, Commented Mar 15, 2020 at 2:15
you're not changing the original array in your code, only accessing array[i][j]. So, array will remain as is. — Nick Parsons
– Nick Parsons, Commented Mar 15, 2020 at 2:21
arrayCop.forEach(element => {if (arrayCop.indexOf(element) < arrayCop.lastIndexOf(element)) {arrayCop[arrayCop.indexOf(element)] = 'something'}}) — Yamil Duba
– Yamil Duba, Commented Mar 15, 2020 at 2:33

NinaW · Accepted Answer · 2020-03-15 03:52:21Z

1

If I understand right, you would like to change the original array to:

[[1, 2], [4, 5], [7, 8]]

If so, this would do it:

array.forEach(element => element.splice(2))

answered Mar 15, 2020 at 3:52

NinaW

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1 Comment

Yamil Duba Over a year ago

No, from the original array I need to create a second flat array containing the first and second items of every file, iterate through this new array and finally that the changes made to this array be reflected on the original one. For example: let arr = [ [1, 2, 3] [4, 5, 6] [7, 8, 9] ]; let newArr = [1, 2, 4, 5, 7, 8]; [do some iteration through newArr here] console.log(arr); // [ ['x', 2, 3] [4, 'x', 6] ['x', 'x', 9] ] Thanks!

2239559319 · Accepted Answer · 2020-03-15 02:17:54Z

0

You can use Array.prototype.map function

answered Mar 15, 2020 at 2:17

2239559319

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Comments

Lapys · Accepted Answer · 2020-03-15 04:14:49Z

0

ORIGINAL

I need to iterate over the first and second element of every nested array and update the changes on the original array

function iterate(array) {
    array.forEach(function(element, index) {
        console.log('[' + index + "][0]", element[0]);
        console.log('[' + index + "][1]", element[1])
    })
}

Not sure what you mean by update changes to the original array, though...

EDIT

Alright, after looking through other answers, I believe @NinaW got what you were looking for.

function parse(array) {
    array.forEach(function(element) { element.slice(0, 2) })
}

edited Mar 15, 2020 at 4:14

answered Mar 15, 2020 at 3:51

Lapys

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Comments

Siva Kondapi Venkata · Accepted Answer · 2020-03-15 09:32:31Z

0

Use flatMap and destructuring.

let array = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];

let arrayCop = array.flatMap(([first, second]) => [first, second]);

console.log(arrayCop)

answered Mar 15, 2020 at 9:32

Siva Kondapi Venkata

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Comments

Yamil Duba · Accepted Answer · 2020-03-16 01:34:19Z

0

let array = [[1, 2, 3], [7, 4, 1], [2, 4, 3]];

console.log(array);

// checks for duplicates just in first and second item of every file
for (let i = 0; i <= 1; i++) {
    for (let j = 0; j <= 2; j++) {
        array[i].forEach((element, index) => {
            if ((i !== j) && index <= 1 &&
            (array[j].indexOf(element) >= 0 && array[j].indexOf(element) <= 1)) {
                array[i][index] = 'x';
            }
        })
    }
}

console.log(array);

answered Mar 16, 2020 at 1:34

Yamil Duba

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