Get largest value in multi-dimensional array javascript or coffeescript

Question

I have an array that looks like the following:

array = [[1, 5], [4, 7], [3, 8], [2, 3],  
 [12, 4], [6, 6], [4, 1], [3, 2], 
 [8, 14]]

What I need is the largest number from the first value of the sets, so in this case 12. Looking at some examples online, the best way I saw to accomplish this is :

Math.max.apply Math, array

Problem is, this only works with single dimensional arrays. How would I impliment this for my senario? (jquery allowed)

The end solution:

It wasn't part of the question, but I needed both the min and max from the array, and that changes things a little.

    unless device.IE
        justTheDates    = magnitudeArray.map (i) -> i[0]
        @earliest       = Math.min.apply Math, justTheDates
        @latest         = Math.max.apply Math, justTheDates                 
    else
        @earliest       = magnitudeArray[0][0]
        @latest         = magnitudeArray[0][0]
        for magnitudeItem in magnitudeArray
            @earliest   = magnitudeItem[0] if magnitudeItem[0] < @earliest
            @latest     = magnitudeItem[0] if magnitudeItem[0] > @latest

2 revs user1106925 · Accepted Answer · 2012-06-22 13:00:43Z

14

You can use .reduce()...

array.reduce(function(max, arr) { 
    return Math.max(max, arr[0]); 
}, -Infinity)

Here's a version that doesn't use Math.max...

array.reduce(function(max, arr) {
    return max >= arr[0] ? max : arr[0];
}, -Infinity);

...and a jsPerf test.

edited Jun 22, 2012 at 13:00

community wiki

2 revs
user1106925

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9 Comments

epidemian Over a year ago

+1 For a classic fold example :). A CoffeeScript translation: max = array.reduce ((max, arr) -> Math.max max, arr[0]), -Infinity

Fresheyeball Over a year ago

I am seeing more votes for this answer. Would someone be interested in making a case for it OVer the one I accepted?

user1106925 Over a year ago

@Fresheyeball: I wouldn't want to say that one is better than the other. A .reduce() just evaluates an Array down to a single value. A .map() is basically a .reduce() that evaluates it down to a new collection. So a .map() behavior can be achieved using .reduce() like this: array.reduce(function(arr, curr) { arr.push(curr[0]); return arr; }, []). And then you'd still use Math.max.apply.... The advantage using the .map() style with .apply is that you avoid the repeated Math.max calls. The advantage of reducing directly to a number is perhaps a little clarity.

Fresheyeball Over a year ago

Interesting. Yeah I found how the shim works and just implemented a loop for ie8-

user1106925 Over a year ago

@tq: return Math.max.apply(Math, arr.concat(max))

|

zerkms · Accepted Answer · 2012-06-22 03:44:07Z

9

http://jsfiddle.net/zerkms/HM7es/

var max = Math.max.apply(Math, arr.map(function(i) {
    return i[0];
}));

So at first you use array.map() to convert the 2-dimensional array to a flat one, and after that use Math.max()

answered Jun 22, 2012 at 3:44

zerkms

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5 Comments

Fresheyeball Over a year ago

I am not familiar with .map can you explain what is going on there?

zerkms Over a year ago

@Fresheyeball: developer.mozilla.org/en/JavaScript/Reference/Global_Objects/… --- so it applies a callback to each element. In your case each i is a [1, 5] - array of 2 elements, and you just return first item. After arr.map() is applied you have another array, that contains 1st elements of each nested array

Fresheyeball Over a year ago

I guess my question is ... is .map more or less efficient than a loop?

zerkms Over a year ago

@Fresheyeball: I'm sure it is very close to it and I'm also sure it is not a thing you need to think about now. Choose the solution you can read/maintain better

numbers1311407 Over a year ago

CoffeeScript often suggests node, but it might be worth noting that Array#map isn't supported <= IE8

epidemian · Accepted Answer · 2012-06-22 04:20:25Z

3

A simple solution using Underscore.js' max that avoids generating an intermediate array:

max = _(array).max(_.first)[0]

(JSFiddle)

answered Jun 22, 2012 at 4:20

epidemian

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2 Comments

Fresheyeball Over a year ago

I am NOT going to include an entire new lib just do solve this.

epidemian Over a year ago

OK, then the other solutions will work better :). Underscore has many useful little functions that, in my experience, are used quite often; and it's only 4KB, so, if it is because of library size, you are not in danger of bloating too much when including it.

jimr · Accepted Answer · 2012-06-22 04:05:11Z

1

Using a comprehension in CoffeeScript:

Math.max.apply Math, (x[0] for x in array)

Running example

edited Jun 22, 2012 at 4:05

answered Jun 22, 2012 at 3:57

jimr

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1 Comment

epidemian Over a year ago

Splats can do the job too: Math.max (x[0] for x in array) ... :)

Community · Accepted Answer · 2017-05-23 11:53:46Z

1

Also, look at _underscore.js. Here is a link to the function _max().

It is simply more efficient to read, write and maintain.

The best part about _underscore is that there are about another hundred helper functions similar to _max. Like sort.

Compare the syntax below:

var sortedObject = _.sortBy(object, function(val, key, object) {
    return val;
});

They are easy to chain, and interpret! (Like Douglas Crockford might suggest)

An excellent JSFIDDLE, was provided in this post by @Raynos.

If you are consistently conducting array operations with raw JavaScript, check out _underscore.js, it can greatly simplify your code.

Hope that helps, All the best! Nash

edited May 23, 2017 at 11:53

CommunityBot

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answered Jun 22, 2012 at 3:57

Nash Worth

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6 Comments

zerkms Over a year ago

"It is simply more efficient" --- how the library can be more efficient than the underlying language?

Nash Worth Over a year ago

Good question, more efficient to write (to read, and maintain). Thanks for the clarification @zerkms. +1. Edited.

Fresheyeball Over a year ago

I am NOT going to include an entire new lib just do solve this.

Nash Worth Over a year ago

Correct. This is for those that are "consistently conducting array operations with raw JavaScript". Some environments are such. If maintaining advanced algorithms this may be an optimization for you. It also comes with a powerful templating engine for advanced data-binding.

Fresheyeball Over a year ago

Frankly I am not impressed with underscore.

|

Sarah-Jane · Accepted Answer · 2013-05-02 09:36:42Z

1

Array.prototype.maxX = function(){
  return Math.max.apply(Math,this.map(function(o){return o[0];}));
};

answered May 2, 2013 at 9:36

Sarah-Jane

1532 silver badges4 bronze badges

Comments

user3051780 · Accepted Answer · 2016-12-18 13:06:27Z

1

I know this is an old post, but if you (or someone else) want the largest number in the whole array, try with:

var array = [[1, 5], [4, 7], [3, 8], [2, 3],  
 [12, 4], [6, 6], [4, 1], [3, 2], 
 [8, 14]];

var max = array.reduce(function (max, arr) {
    return max >= Math.max.apply(max, arr) ? max : Math.max.apply(max, arr);
}, -Infinity);
console.log(max);

In this examlpe, it will return the value 14.

answered Dec 18, 2016 at 13:06

user3051780

Comments

dorgo · Accepted Answer · 2016-08-01 19:58:52Z

0

Sample Input: largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);

function largestOfFour(arr) {

    var largest = 0;
    var largestArr = [];
    for(var i=0; i<arr.length; i++){
      for(var j=0; j<arr[i].length; j++){

        if(largest < arr[i][j]){
          largest = arr[i][j];
        }
        largestArr[i] = largest;
      }      
      largest = 0;
    }

  return largestArr;
}

You can populate largest numbers into new Array from two dim array.

answered Aug 1, 2016 at 19:58

dorgo

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Comments

MichaelG · Accepted Answer · 2021-08-31 02:17:23Z

0

ES2019 Array.prototype.flat() with destructuring.

const max = Math.max(...arr.flat());

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

answered Aug 31, 2021 at 2:17

MichaelG

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