Returning array of largest numbers

Question

I have this little script that will return the largest number of an array, it works, except it doesn't work for multidimensional arrays.

How can I tweak this to return an array of the largest numbers within a multidimensional array?

Source:

function largestOfFour(arr) {
    for(var x=0;x < arr.length; x++){
        var largest = Math.max.apply(Math, arr[x]);
        return largest;
    }
}

Example:

> function largestOfFour(arr) {
...     for(var x=0;x < arr.length; x++){
.....         var largest = Math.max.apply(Math, arr[x]);
.....         return largest;
.....     }
... }
undefined
> largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);
5
>

Expected output:

[5, 27, 39, 1001]

the for loop can be replaced with `var largest = Math.max.apply(Math, arr);`. — Nina Scholz, Apr 29 '16 at 13:51
@lipp I am not, but I am willing to learn? And yes the depth stays that same as the example — 13aal, Apr 29 '16 at 13:52
@Tushar Woah, you're right that's literally the same question — 13aal, Apr 29 '16 at 13:53
[`arr.map(Math.max.apply.bind(Math.max, null))`](http://stackoverflow.com/a/32679435/2025923) **That's it** — Tushar, Apr 29 '16 at 13:53
please have a look to another reference of apply.bind http://stackoverflow.com/questions/34747551/foreach-and-apply-methods-for-two-dimensional-array-javascript/34747724#34747724 — Nina Scholz, Apr 29 '16 at 14:02

score 2 · Answer 1 · edited Apr 29 '16 at 14:11

2

You can use ES6 arrow function and spread operator.

arr.map(e => Math.max(...e))

map will iterate(i.e. nested arrays) over all the elements of main array and Math.max(...e) will return the max element of that array. The ...e will pass the elements of e array individually to the max().

var arr = [ [4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1] ]

var res = arr.map(e => Math.max(...e))

document.write(res);

edited Apr 29 '16 at 14:11

Tushar

85,780
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179

answered Apr 29 '16 at 14:04

isvforall

8,768
6
35
50

1

I really like that. :) – Tushar Apr 29 '16 at 14:09

Nina Scholz · Accepted Answer · 2016-04-29T14:04:28.740

1

Just map the result of the single results.

function largestOfFour(array) {
    return array.map(function (a) {
        return Math.max.apply(null, a);
    });
}

var largest = largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);
document.write('<pre>' + JSON.stringify(largest, 0, 4) + '</pre>');

The above mentioned (@Tushar) short version

function largestOfFour(array) {
    return array.map(Math.max.apply.bind(Math.max, null));
}

var largest = largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);
document.write('<pre>' + JSON.stringify(largest, 0, 4) + '</pre>');

edited Apr 29 '16 at 14:04

answered Apr 29 '16 at 13:53

Nina Scholz

376,160
25
347
392

3

[Can be shortened](http://stackoverflow.com/questions/36940109/returning-array-of-largest-numbers#comment61439382_36940109) – Tushar Apr 29 '16 at 13:54
This makes perfect sense, thank you. – 13aal Apr 29 '16 at 14:04
@Tushar ever shorter `arr.map(e => Math.max(...e))` – isvforall Apr 29 '16 at 14:04
@isvforall ES6, yaay! Updated my answer. Thanks :) – Tushar Apr 29 '16 at 14:07

Returning array of largest numbers

2 Answers2