Javascript: Turn a nested array into a single array using a nested for loop

Question

This is just a simple javascript exercise that I'm working on.

I'm trying to convert this array...

var array = [
[1,2],
[3,4],
[5,6]
];

into...

array = [1, 2, 3, 4, 5, 6];

by using this nested for loop.

var series;
var storage = [];
for (var i = 0; i < array.length; i++) {
    for (var j = 0; j < array[i].length; j++) {
        series = array[i][j];
        for (var k = 0; k < 6; k++) {
            storage[k] = series;
        };
    };
};

console.log(storage);

With an output of...

//Output: [6, 6, 6, 6, 6, 6]

Why is this the output and how can I fix it?

brk · Accepted Answer · 2018-11-22 16:26:02Z

2

for (var k = 0; k < 6; k++) { is not required . array[i] will be each of element inside main array , so iterating over array[i] you can access each of the element

var array = [
  [1, 2],
  [3, 4],
  [5, 6]
];


var series;
var storage = [];
for (var i = 0; i < array.length; i++) {
  for (var j = 0; j < array[i].length; j++) {
    storage.push(array[i][j])
  };
};

console.log(storage);

answered Nov 22, 2018 at 16:26

brk

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Comments

bipll · Accepted Answer · 2018-11-22 16:23:15Z

2

    series = array[i][j];
    for (var k = 0; k < 6; k++) {
        storage[k] = series;
    };

Seriously, here you set the same value to each element of the resulting array.

You probably need something like

for(let x of array) {
    for(let y of x) {
        storage.push(y)
    }
}

Or, if your JS machine is experimental enough, simply

var storage = array.flat()

answered Nov 22, 2018 at 16:23

bipll

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Comments

George · Accepted Answer · 2018-11-22 16:25:52Z

1

You can use a mix of reduce and concat to achieve what you want in one line

var array = [
  [1, 2],
  [3, 4],
  [5, 6]
];

console.log(array.reduce((a, v) => a.concat(v), []));

As for why your code didn't work, it's mainly down to this bit

for (var k = 0; k < 6; k++) {
    storage[k] = series;
};

It would overwrite everything in the array with the last value of series, which in your case would be 6

answered Nov 22, 2018 at 16:25

George

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Comments

SpeedOfRound · Accepted Answer · 2018-11-22 16:26:50Z

1

Array.concat can do this on its own

var merged = [].concat.apply([], array);

answered Nov 22, 2018 at 16:26

SpeedOfRound

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Comments

Ayon Saha · Accepted Answer · 2018-11-22 16:28:55Z

1

var array = [
[1,2],
[3,4],
[5,6]
];
var newArray = [];
for (let i = 0; i < array.length; i++) {
   newArray = newArray.concat(array[i]); 

}
console.log(newArray)

answered Nov 22, 2018 at 16:28

Ayon Saha

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Comments

Christheoreo · Accepted Answer · 2018-11-22 16:24:47Z

0

You can use array.flat()

Reference : flatten

var array = [
  [1,2],
  [3,4],
  [5,6]
];
array.flat();
// 1,2,3,4,5,6....

answered Nov 22, 2018 at 16:24

Christheoreo

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Comments

weibenfalk · Accepted Answer · 2018-11-22 16:25:24Z

0

You could use the ES6 spread syntax like this:

for (let element of array){
    storage.push( ... el )
}

answered Nov 22, 2018 at 16:25

weibenfalk

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Comments

bugpulver · Accepted Answer · 2018-11-22 16:32:10Z

0

storage = [];
for(var i=0; i<array.length; i++)
    storage = storage.concat(array[i]);

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/concat

answered Nov 22, 2018 at 16:32

bugpulver

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