DEV Community

Returning an object using reduce()

PJ Mantoss on March 06, 2020

Hi good people! I need help with some JavaScript challenge: QUESTION: Write a function called getSongCountByArtist which takes in an array of song...

Read full post

Craig McIlwrath • Mar 6 '20

You're code is very close, but the function given to reduce should return an object. Instead of returning acc[val.artist] + songNo, you could increment acc[val.artist] by songNo and the return acc.

Although I'm not sure why you're adding the length of the song name. Maybe just increment by 1 each time?

PJ Mantoss • Mar 6 '20

Hi Craig! I have applied your suggestion. It's still not returning the right data. It returns an empty object. Please See below:

function getSongCountByArtist(arr){

return arr.reduce(function(acc,val){
    let artistName = val.artist,
        artistSong = val.name;

     arr[artistName] = artistSong;

    if(artistName){
        artistSong += 1;
    }

    return acc;

}, {})

}
//test
getSongCountByArtist(songs); // {}

Thank you

Craig McIlwrath • Mar 6 '20

Seems I didn't describe my idea very well. Here's the code I had in mind:

function getSongCountByArtist(songs) {
  return songs.reduce(function (acc, song) {
    if (acc[song.artist] === undefined) acc[song.artist] = 0;
    acc[song.artist]++;
    return acc;
  }, {});
}

PJ Mantoss • Mar 7 '20

Hello Craig! I've implemented your code and it works perfectly now. Thanks a million! I appreciate your help.

EddiFd • Mar 6 '20

Do not use reduce.

Try :

Array.from(new Set(songs.map(e => e.artist).sort()).values()).map(e => {let obj = {}; obj[e] = songs.filter(f => f.artist == e).length; return obj;})