Challenge Task : Using the reduce method, extract all the customer hobbies into their own array. Store the hobbies

Hi Anik!

In case you haven't solved this yet:

You are really close. There was one thing that you missed was when you were attempting to iterate over to the embedded hobbies array: you first need to get to the personal key/property before you can traverse further down into the embedded hobbies property/array.

Your map method should look like this:

.map(customer => customer.personal.hobbies.map(hobby => hobby))

Than you can initiate the reduce method like so:

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

I hope that this helps. This one had me stumped for a bit too.

Cheers:-)

I had to read the MDN docs on array.prototype.reduce() to figure out the answer for this problem. There is a relevant section labeled "Bonding arrays contained in an array of objects using the spread operator and initialValue". The documentation can be found here https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce?v=a

If reduce is written like this, it can't find "hobbies":

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

Instead, write the reduce method like this:

.reduce((prev, curr) => [...prev, ...curr.personal.hobbies], []);

The nested "map" functions aren't necessary (and causing syntax errors). Much like the previous challenge, the "reduce" by itself is enough to solve the challenge, but this time you need to extract the correct properties from each item.

I'll bet you can get it now without an explicit spoiler.

The task ask you to use the reduce method. Here is how I solved it.

hobbies = customers.reduce((accumulator, currentValue)=> {
  return [...accumulator, ...currentValue.personal.hobbies]
}, []);

Here is the link to the documentation I use to solve it. (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce#bonding_arrays_contained_in_an_array_of_objects_using_the_spread_operator_and_initialvalue)

Where did folks learn about using the ellipsis prior to acc and curr? I attempted to write my solution as hobbies = customers.reduce((acc, curr) => [acc, curr.personal.hobbies], []); I don't remember seeing anything in the instructional videos that mentions ellipsis. I'm wondering if I missed something? If anyone has a good resource for explaining the use of ... in this context, please share! I did a little bit of googling but struggled to find a resource that helped me understand.

Hi Chelsea!

When I run this code:

hobbies = customers.map(user => user.personal.map(hobby => hobby.hobbies))
         .reduce((arr, allHobbies) => [...arr, ...allHobbies], []);

...I get this error:

TypeError: user.personal.map is not a function

What this is trying to say is that the map function` will not map over an object (in this case, user.personal is an object) directly. The map method is meant to iterate over arrays, so in order to iterate over the hobbies field, try accessing the field with a more direct approach like so:

hobbies = customers.map(user => user.personal.hobbies.map(hobby => hobby))
            .reduce((arr, allHobbies) => [...arr, ...allHobbies], []);

Notice that I mapped over user.personal.hobbies (because hobbies is an array) & I also removed hobbies from map(hobby => hobby.hobbies)). The main thing to remember is that the map method is meant to work with arrays.

I hope that this helps and makes sense.

Cheers:-)