Using Reduce method

Question

I just started learning about reduce method, and stuck in this problem...

  N   answer
123   6
987   24

An example would be 9 + 8 + 7 = 24 but the parameter is in number.

Here is what I have tried:

function solution (n){
   let result = new Array (n)
   let answer = result.reduce((a,b) => {
       return a + b 
   })
}

Here is my code but I'm getting TypeError [Error]: Reduce of empty array with no initial value

you instantiated an empty array of size n. It doesn't contains anything. You input is a string so convert it to a array of char n.split('') or [...n] or Array.from(n) then you can do map to int and use your reduce operation — JEY, Nov 15 '21 at 17:20
Does this answer your question? [How to find the sum of an array of numbers](https://stackoverflow.com/questions/1230233/how-to-find-the-sum-of-an-array-of-numbers) — Randy Casburn, Nov 15 '21 at 17:20
this-> `(''+123).split('').reduce((acc,n)=>acc+=parseInt(n),0);` — Randy Casburn, Nov 15 '21 at 17:25

score 1 · Answer 1 · answered Nov 15 '21 at 17:28

1

Here's how you would use reduce to calculate the sum -

[...String(123)].map(Number).reduce((a,b) => a+b, 0)

answered Nov 15 '21 at 17:28

chunkydonuts21

Wow, I love this. Please elaborate and explain to the OP *why* this works. – Michael Haddad Nov 15 '21 at 17:41
Also, I believe you don't need the `0`. – Michael Haddad Nov 15 '21 at 17:41

score 0 · Answer 2 · answered Nov 15 '21 at 17:33

This:

let result = new Array (n)

creates an empty array with a length of n.

In order to convert a number to an array of digits, you can use this little handy snippet:

const arr = n.toString().split('').map(Number)

We are getting n as a string, then splitting it into an array of characters, and then mapping each character to its corresponding digit.

After that you can use the reduce function:

let answer = arr.reduce((a,b) => {
    return a + b 
});

2 Answers2