javascript tutorial - [Solved-5 Solutions] Merge/flatten an array of arrays in javascript - javascript - java script - javascript array

We have a JavaScript array like:

[["$6"], ["$12"], ["$25"], ["$25"], ["$18"], ["$22"], ["$10"]]

How would we go about making this just:

["$6", "$12", "$25", ...]

We can use concat to merge arrays:

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

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

var merged2 = [].concat(["$6"], ["$12"], ["$25"], ["$25"], ["$18"], ["$22"], ["$10"]);

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]

Here's a simple and performant functional solution:

var result = [].concat.apply([], [[1],[2,3],[4]]);
console.log(result); // [ 1, 2, 3, 4 ]

It can be best done by javascript reduce function.

var arrays = [["$6"], ["$12"], ["$25"], ["$25"], ["$18"], ["$22"], ["$10"], ["$0"], ["$15"],["$3"], ["$75"], ["$5"], ["$100"], ["$7"], ["$3"], ["$75"], ["$5"]];

arrays = arrays.reduce(function(a, b){
     return a.concat(b);
}, []);

Or, with ES2015:

arrays = arrays.reduce((a, b) => a.concat(b), []);

We can use Underscore :

var x = [[1], [2], [3, 4]];

_.flatten(x); // => [1, 2, 3, 4]