javascript array flatten example

stackoverflow.com › questions › 10865025 › merge-flatten-an-array-of-arrays

ES2019

ES2019 introduced the Array.prototype.flat() method which you could use to flatten the arrays. It is compatible with most environments, although it is only available in Node.js starting with version 11, and not at all in Internet Explorer.

const arrays = [
      ["12"],
      ["25"],
      ["22"],
      ["$10"]
    ];
const merge3 = arrays.flat(1); //The depth level specifying how deep a nested array structure should be flattened. Defaults to 1.
console.log(merge3);

Older browsers

For older browsers, you can use Array.prototype.concat to merge arrays:

var arrays = [
  ["12"],
  ["25"],
  ["22"],
  ["$10"]
];
var merged = [].concat.apply([], arrays);

console.log(merged);

Using the apply method of concat will just take the second parameter as an array, so the last line is identical to this:

var merged = [].concat(["$6"], ["$12"], ["$25"], ["$25"], ["$18"], ["$22"], ["$10"]);

Answer from Gumbo on Stack Overflow

MDN Web Docs

developer.mozilla.org › en-US › docs › Web › JavaScript › Reference › Global_Objects › Array › flat

Array.prototype.flat() - JavaScript - MDN Web Docs

However, its elements must be arrays if they are to be flattened. ... const arr1 = [1, 2, [3, 4]]; arr1.flat(); // [1, 2, 3, 4] const arr2 = [1, 2, [3, 4, [5, 6]]]; arr2.flat(); // [1, 2, 3, 4, [5, 6]] const arr3 = [1, 2, [3, 4, [5, 6]]]; arr3.flat(2); // [1, 2, 3, 4, 5, 6] const arr4 = [1, 2, [3, 4, [5, 6, [7, 8, [9, 10]]]]]; arr4.flat(Infinity); // [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] ... const arr5 = [1, 2, , 4, 5]; console.log(arr5.flat()); // [1, 2, 4, 5] const array = [1, , 3, ["a", , "c"]]; console.log(array.flat()); // [ 1, 3, "a", "c" ] const array2 = [1, , 3, undefined, ["a", , ["d", , "e"]], null]; console.log(array2.flat()); // [ 1, 3, undefined, "a", ["d", empty, "e"], null ] console.log(array2.flat(2)); // [ 1, 3, undefined, "a", "d", "e", null ]

Stack Overflow

stackoverflow.com › questions › 10865025 › merge-flatten-an-array-of-arrays

javascript - Merge/flatten an array of arrays - Stack Overflow

ES2019

ES2019 introduced the Array.prototype.flat() method which you could use to flatten the arrays. It is compatible with most environments, although it is only available in Node.js starting with version 11, and not at all in Internet Explorer.

const arrays = [
      ["12"],
      ["25"],
      ["22"],
      ["$10"]
    ];
const merge3 = arrays.flat(1); //The depth level specifying how deep a nested array structure should be flattened. Defaults to 1.
console.log(merge3);

Older browsers

For older browsers, you can use Array.prototype.concat to merge arrays:

var arrays = [
  ["12"],
  ["25"],
  ["22"],
  ["$10"]
];
var merged = [].concat.apply([], arrays);

console.log(merged);

Using the apply method of concat will just take the second parameter as an array, so the last line is identical to this:

var merged = [].concat(["$6"], ["$12"], ["$25"], ["$25"], ["$18"], ["$22"], ["$10"]);

2 of 16

615

Here's a short function that uses some of the newer JavaScript array methods to flatten an n-dimensional array.

function flatten(arr) {
  return arr.reduce(function (flat, toFlatten) {
    return flat.concat(Array.isArray(toFlatten) ? flatten(toFlatten) : toFlatten);
  }, []);
}

Usage:

flatten([[1, 2, 3], [4, 5]]); // [1, 2, 3, 4, 5]
flatten([[[1, [1.1]], 2, 3], [4, 5]]); // [1, 1.1, 2, 3, 4, 5]

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