Return the largest Array

Question

I've been trying to solve this practice problem:

Return an array consisting of the largest number from each provided sub-array. For simplicity, the provided array will contain exactly 4 sub-arrays.

But my code only returns the single element of from the whole array, if I unshift all the max elements it produces totally wrong results, I tried to execute the nested loop separately and it worked fine but it creates a problem when combined with outer loop.

function largestOfFour(arr)
{
    // You can do this!
    var max = 0;
    var largestArray =[];
    for (var i = 0; i <4; i++)
    {
        for (var j = 0; j <4; j++)
        {
            if (arr[i][j]>max)
            {
              max=arr[i][j];
              largestArray.unshift(max);
              //console.log(max);
            }

        }
    }
      console.log(largestArray);
    return max;
}

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

Before anyone else adds Math.max answers the OP would like help with the code they've written. — Andy
– Andy, Commented Oct 2, 2017 at 9:03

Ori Drori · Accepted Answer · 2017-10-02 09:14:07Z

How to fix your code (see comments in code):

function largestOf(arr) {
  var max;
  var largestArray = [];

  for (var i = 0; i < arr.length; i++) { // the arr length is the number of sub arrays
    max = -Infinity; // max should be reinitialized to the lowest number on each loop
    for (var j = 0; j < arr[i].length; j++) { // the length is the number of items in the sub array
      if (arr[i][j] > max) { // just update max to a higher number
        max = arr[i][j];
      }
    }
    
    largestArray.push(max); // push max after the internal loop is done, and max is known
  }

  return largestArray; // return the largest array
}

var result = largestOf([[4, 5, 1, 13], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);

console.log(result);

Another solution is to use Array#map, and apply Math#max to each sub array to get it's maximum value:

function largestOf(arr) {
  return arr.map(function(s) {
    return Math.max.apply(Math, s);
  });
}

var result = largestOf([[4, 5, 1, 13], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);

console.log(result);

marvel308 · Accepted Answer · 2017-10-02 08:59:09Z

1

You can do

function largestOfFour(arr)
{
    return arr.map(e => Math.max(...e));
}

let result = largestOfFour([[4, 5, 1, 13], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);

console.log(result);

answered Oct 2, 2017 at 8:59

marvel308

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3 Comments

Ahsan Alii Over a year ago

I worked fine, but can you please figure-out whats wrong with my code ?

artgb Over a year ago

I saw a very interesting format '...e' can you explain about it?

marvel308 Over a year ago

@artgb you can take a look at developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…

StackSlave · Accepted Answer · 2017-10-02 09:12:04Z

0

Hopefully this helps:

var pre = onload, largestOfFour; // for use on other loads
onload = function(){
if(pre)pre(); // change var pre name if using technique on other pages

function largestOfFour(arrayOfFours){
  for(var i=0,a=[],l=arrayOfFours.length; i<l; i++){
    a.push(Math.max.apply(null, arrayOfFours[i]));
  }
  return a;
}
console.log(largestOfFour([[4, 5, 1, 13], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]));

}

answered Oct 2, 2017 at 9:12

StackSlave

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