Flatten array to 2D

Question

I know there are a couple of answers on the matter, but as I was trying to make my own, I got very lost on how recursive functions work, here's what I tried :

function flatcoords(arr) {
  for (i = 0; i < arr.length; i++) {
    const value = arr[i];
    if (value.isArray) {
      return flatcoords(value);
    } else {
      return arr;
    }
  }

}

const arr_test = [
  [
    [1, 2],
    [1, 2]
  ],
  [1, 2],
  [1, 2],
  [
    [
      [1, 2],
      [1, 2]
    ]
  ]
];

//wanted_result = [ [1,2],[1,2],[1,2],[1,2],[1,2],[1,2] ]
console.log(flatcoords(arr_test));

I want the result to be a 2D array, what am I missing in my logic?

[1, 2][? shouldn't there be a comma after ]?

gurvinder372
– gurvinder372

2017-12-05 18:48:26 +00:00
Commented Dec 5, 2017 at 18:48 — gurvinder372
– gurvinder372, Commented Dec 5, 2017 at 18:48
@gurvinder372 oops, fixed, thanks

Mojimi
– Mojimi

2017-12-05 18:49:36 +00:00
Commented Dec 5, 2017 at 18:49 — Mojimi
– Mojimi, Commented Dec 5, 2017 at 18:49

Nina Scholz · Accepted Answer · 2017-12-05 19:19:17Z

3

First of all, you need to declare all variables before use. Then you could use Array.isArray for a check if an item is an array.

In this case, I suggest to check the first item of the checked element if it is an array as well, in this case flat the array.

As result, an array comes in handy, because not only one element should be returned, but all. And while arrays have more item, you need to append all items to the existing result array.

function flatcoords(array) {
    var result = [],
        value,
        i;

    for (i = 0; i < array.length; i++) {
        value = array[i];
        if (Array.isArray(value) && Array.isArray(value[0])) {
            result = result.concat(flatcoords(value));
        } else {
            result.push(value);
        }
    }
    return result;
}

const arr_test = [[[1, 2], [1, 2]], [1, 2], [1, 2], [[[1, 2], [1, 2]]]];

console.log(flatcoords(arr_test));

.as-console-wrapper { max-height: 100% !important; top: 0; }

edited Dec 5, 2017 at 19:19

answered Dec 5, 2017 at 18:56

Nina Scholz

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2 Comments

Carl Edwards Over a year ago

What stops result from being reset to an empty array once you recursively call the function?

Nina Scholz Over a year ago

@CarlEdwards, at least, you get the elment or the inner array.

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