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JavaScript JavaScript Array Iteration Methods Combining Array Methods Nested Data

Benjamin Stano
Benjamin Stano
2,742 Points
Posted by Benjamin Stano
Benjamin Stano
2,742 Points

Array Flattening Methods Challenge Question

I am having trouble figuring out how to flatten the strings using only the reduce method. I tried to emulate the method the teacher in the video used for the similar problem, where he called '.map' twice in once {{e.g. hobbies = customers.map(customers => customer.personal.map(person => person.hobbies))}} and then calling reduce on it. But it doesn't seem to work here. I have tried looking at other resources but I feel very lost right now.

app.js 
const customers = [
  {
    name: "Tyrone",
    personal: {
      age: 33,
      hobbies: ["Bicycling", "Camping"]
    }
  },
  {
    name: "Elizabeth",
    personal: {
      age: 25,
      hobbies: ["Guitar", "Reading", "Gardening"]
    }
  },
  {
    name: "Penny",
    personal: {
      age: 36,
      hobbies: ["Comics", "Chess", "Legos"]
    }
  }
];
let hobbies;

// hobbies should be: ["Bicycling", "Camping", "Guitar", "Reading", "Gardening", "Comics", "Chess", "Legos"]
// Write your code below
hobbies = customers.reduce((arr, hobby) => arr.concat(hobby), []);

console.log(hobbies);
Benjamin Stano
Benjamin Stano
2,742 Points
Benjamin Stano
Benjamin Stano
2,742 Points

Code I tried to emulate: const books = users .map(user => user.favoriteBooks.map(book => book.title)) .reduce((arr, titles) => [...arr, ...titles],[]);

Code I wrote: hobbies = customers .map(cust => cust.personal.map(person => person.hobbies)) .reduce((arr,hobby) => [...arr,...hobby], []);

Was I wrong to try to emulate his method here? I've seen that I could do this only using the reduce method, but I don't feel confident enough with reduce to know how. Help is much appreciated.

1 Answer

Steven Parker
Steven Parker
231,269 Points
Steven Parker
Steven Parker
231,269 Points

You have the right idea to use the spread operator to combine arrays, but you don't need to use "map" if you reference the member of the object that stores the hobbies directly in the callback function.

You can't call "cust.personal.map" anyway, because "map" is an array method, but "cust.personal" is an object.

Benjamin Stano
Benjamin Stano
2,742 Points
Benjamin Stano
Benjamin Stano
2,742 Points

Ooh, that makes a lot of sense. But, I'm not sure how I would reference the object member in the callback function. I feel like the video in this course didn't tell me a lot about the spread operator or the reduce function. Something like?:

hobbies = customers.reduce((arr,person) => [...arr,...person.personal.hobbies], []);

Steven Parker
Steven Parker
231,269 Points
Steven Parker
Steven Parker
231,269 Points

Exactly like that, good job! :+1: Use that code and pass the challenge.