how to return the two largest number from each array of an array in JavaScript without using for loops?

Question

    function theHighest(data) {
        let twoLargest = data.map((x) => {
            return x.reduce((prev, curr) => {
                return curr
            })
        })
        return twoLargest //returns [3,5,8]
    
    }
    console.log(theHighest([[1, 2, 3], [3, 4, 5], [6, 7, 8]]))

The above function can return the largest numbers in each array and if it could return prev along with curr in the same array the job would be done and the desired result would be achieved which is [2,3,4,5,7,8] How can I return this without using for loops at all?

If I use for loops here is how I do it:

    function theHighest(data) {
        let highestValues = []
    
        for (let i = 0; i < data.length; i++) {
            let first = 0
            let second = 0
             
            for (let j = 0; j < data[i].length; j++) {
                    if (first < data[i][j]) {                  
                        second = first;
                        first = data[i][j];
                    }
                    else if (second < data[i][j]) {                   
                        second = data[i][j];
                    }
    
            }
            highestValues.push(first, second)
        }    
    return highestValues
        }
    console.log(theHighest([[1, 2, 3], [3, 4, 5], [6, 7, 8]]))

Thank you!

The first function does not return the largest number of each array, it returns the last number (which is different in general unless the arrays are already sorted). — Thilo
– Thilo, Commented Feb 12, 2018 at 10:13
Either way, that prev in your reduce function is the output of the previous iteration. You can set it to an array of the largest two numbers so far. — Thilo
– Thilo, Commented Feb 12, 2018 at 10:14
If the arrays are indeed already sorted, you can map a slice that takes the last two entries. — Thilo
– Thilo, Commented Feb 12, 2018 at 10:18

Nina Scholz · Accepted Answer · 2018-02-12 10:18:40Z

2

You could take a copy, sort the array and return the two max values.

function theHighest(data) {
    return [].concat(...data.map(a => a.slice().sort((a, b) => a - b).slice(-2)));
}

console.log(theHighest([[1, 2, 3], [3, 4, 5], [6, 7, 8]]));

answered Feb 12, 2018 at 10:18

Nina Scholz

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1 Comment

georg Over a year ago

or just [...a].sort() ;)

void · Accepted Answer · 2018-02-12 10:28:02Z

2

You need to sort the array as well if it not sorted

function theHighest(data) {
        let twoLargest = data.map((x) => {
            // Get two largest integers
            return x.sort().slice(-2);
        })
        // Flatten the array
        return Array.prototype.concat(...twoLargest);
    
    }
   
    console.log(theHighest([[1, 2, 3], [3, 4, 5], [6, 7, 8]]))

edited Feb 12, 2018 at 10:28

answered Feb 12, 2018 at 10:21

void

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1 Comment

void Over a year ago

@Thilo ah ignore that.

gurvinder372 · Accepted Answer · 2018-02-12 10:19:33Z

1

You can also use reduce and sort

var output = arr.reduce( (a, c) => a.concat(c.sort().slice(-2)), [] );

outputs [2,3,4,5,7,8]

Demo

var arr = [[1, 2, 3], [3, 4, 5], [6, 7, 8]];

var output = arr.reduce( (a, c) => a.concat(c.sort().slice(-2)), [] );

console.log( output );

edited Feb 12, 2018 at 10:19

answered Feb 12, 2018 at 10:13

gurvinder372

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4 Comments

Rajesh Dixit Over a year ago

I'm sure I have seen this approach before. Sure you don't want to look around and mark it as dupe if this is the ideal solution?

gurvinder372 Over a year ago

@Thilo That is exactly what my answer does.. It returns [3.5.8] which is the largest of each array

gurvinder372 Over a year ago

@Rajesh Sure looking for one... If I find exact duplicate I will delete this one

gurvinder372 Over a year ago

@Thilo Thanks for pointing out, didn't spotted it first time... it was there in the title itself.

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