Question

89

JavaScript - Return value from array with map function

rated 0 times [ 95] [ 6] / answers: 1 / hits: 5295 / 9 Years ago, wed, november 25, 2015, 12:00:00

I want to extract the largest number of every single array. I believe it should be possible with the .map function.

This is what I have so far, but unfortunately this returns [ undefined, undefined, undefined, undefined ]

Code:

function largestOfFour(largestOfFour) {

    largestOfFour.forEach(function(number){

        number.sort(function(a, b){

            return b - a;

        });

        highestValue = number.map(function(number){

            return number[0];

        });

    });

};



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

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1 Year ago

answered 9 Years ago nicholas · Accepted Answer

You're iterating over the outer array,

function largestOfFour(largestOfFour) {

    largestOfFour.forEach(function(number){

and then sorting the inner arrays,

number.sort(function(a, b){

    return b - a;

});

and then of those inner arrays you're trying to acquire the [0] property from each value, which is undefined

highestValue = number.map(function(number){

// you redefine `number` here to be the value within the inner array

    return number[0];

});

What you probably want to do is map the outer array:

function largestOfFour(largestOfFour) {

    largestOfFour.map(function(numbers){

sort the inner arrays:

numbers.sort(function(a, b){

    return b - a;

});

and then return the first value:

return numbers[0];

All together it probably should be:

function largestOfFour(largestOfFour) {

    return largestOfFour.map(function(numbers){

        numbers.sort(function(a, b){

            return b - a;

        });

        return numbers[0];

    });

}

Although there are simpler ways to find the maximum values of an array of arrays.

One such example is to use Array.prototype.reduce:

function largestValues(outer) {

    return outer.map(function (inner) {

        return inner.reduce(function (prev, current) {

            return Math.max(prev, current);

        }, Number.NEGATIVE_INFINITY);

    });

}