Can someone explain the code to me

JavaScript
1 
function totalVolume(...boxes) {
return boxes.reduce((a,b)=> a + b.reduce((c,d)=> c * d,1),0);
}
console.log(totalVolume([4, 2, 4], [3, 3, 3], [1, 1, 2], [2, 1, 1]))

the question was
Given an array of boxes, create a function that returns the total volume of all those boxes combined together. A box is represented by an array with three elements: length, width and height.

For instance, totalVolume([2, 3, 2], [6, 6, 7], [1, 2, 1]) should return 266 since (2 x 3 x 2) + (6 x 6 x 7) + (1 x 2 x 1) = 12 + 252 + 2 = 266.
Please try to be specific

2

I’ve edited your post for readability. When you enter a code block into a forum post, please precede it with a separate line of three backticks and follow it with a separate line of three backticks to make it easier to read.

You can also use the “preformatted text” tool in the editor (</>) to add backticks around text.

Pre-formatted-text
Pre-formatted-text1356Ă—380 401 KB

See this post to find the backtick on your keyboard.
Note: Backticks (`) are not single quotes (’).

3

Do you have a question?

4

thanks for the edit

my question was
i didnt get that reduce method clearly,i just dont know how the code exactly working behind the scene

5

Seems to me you may be over-thinking a little. Reduce works well here, yes - but you only really need one or maybe two reduce functions.

Suppose we had a similar situation, but let’s say area rather then volume. We are given a two value array for each square, [3,14], and we need an inner function to calculate that. Just do the function for one thing first:

const area = ([length, width]) => {
  return length*width
}

Now, we have a function we can use in a reducer:

const totalArea=rectangles.reduce( (accumulator, rectangle) => {
  return accumulator + area(rectangle)
}, 0)

Only really needed one reduce for the outermost array. If the ([length, width]) part confused, there is a great fcc lesson on array deconstruction (I’m on my phone, or I’d find it for you).

1 Like
6

The “at most two reduce” is mentioned might be to write a product reducer function:

const product = (arrayOfNums) => arrayOfNums.reduce( (product, number) => product*number, 1)

That one takes an array of numbers, and turns it to a product of all the numbers. To use that, you would use that inside the other one:

const totalArea = rectangles.reduce( (accumulator, rect) => accumulator+product(rect), 0)

But, by only defining a single reduce function at a time…way less confusing.

1 Like
7

I get it now,I am not very comfortable with reduce yet.So when i saw the double reduce function in a single line i got really confused,Btw thank you for the explanation.

8

also would you please be kind enough to find me the lesson about array deconstruction

9

but if you google array destructuring you find many different explanations

2 Likes
10

See now? @ilenia is the BEST! Thank you for that.

We could have done that without the deconstruction, simply using the array indices inside our function, but i find the “let’s turn our array into individual values” to be easier to write, and understand… With practice.

1 Like