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# Return Largest Numbers in Arrays - JavaScript Solution & Walkthrough

## (05/16) Learn how to solve coding challenges using FreeCodeCamp's curriculum.

Benjamin Semah
·Apr 5, 2022·

• 05/16 Return Largest Numbers in Arrays
• Understanding the Challenge
• Pseudocode
• Solving the Challenge
• Final Solution
• Congratulations!

## 05/16 Return Largest Numbers in Arrays

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

Remember, you can iterate through an array with a simple for loop, and access each member with array syntax `arr[i]`.

``````function largestOfFour(arr) {

return arr;
}

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

Credit: FreeCodeCamp.org

## Understanding the Challenge

In this challenge, you will be provided with an array containing 4 sub-arrays. Your task is to create a function that return a new array. This new array should contain the largest numbers found in each of the sub-arrays.

## Pseudocode

``````Given an array of sub-arrays
iterate through the array
For each iteration
return the largest number in the sub-array
Return an array of all largest numbers
``````

## Solving the Challenge

So here, we have a given array of sub-arrays. We need to iterate through this given array. There are a number of ways to do so. To keep things simple, let's use the `.map()` method.

We'll map through the given array. For every iteration, we'll have a `subArray` available to us. Using `Math.max()`, we can return the largest number in each `subArray`.

``````  const largeNums = arr.map(subArray => {
return Math.max(...subArray);
})
``````

Note: We are using the `...` spread operator to get all the numbers in the `subArray`.

Using the .map() method, we will get a new array made up of the the large numbers in each sub array.

We can then return this new array, in this case `largeNums` and our function is complete!

``````return largeNums;
``````

## Final Solution

``````function largestOfFour(arr) {
const largeNums = arr.map(subArray => {
return Math.max(...subArray);
})
return largeNums;
}

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

## Congratulations!

You just cracked the fifth challenge in this series.

Cheers and happy coding!