Use the reduce Method to Analyze Data -

JavaScript
1

Tell us what’s happening:

I’m stuck. I was trying to do an average with reduce this way (I kept only 3 of the entries of the object to be able to post):

Your code so far


// the global variable
var watchList = [
                 {  
                   "Title": "Inception",
                   "Year": "2010",
                   "Rated": "PG-13",
                   "Released": "16 Jul 2010",
                   "Runtime": "148 min",
                   "Genre": "Action, Adventure, Crime",
                   "Director": "Christopher Nolan",
                   "Writer": "Christopher Nolan",
                   "Actors": "Leonardo DiCaprio, Joseph Gordon-Levitt, Ellen Page, Tom Hardy",
                   "Plot": "A thief, who steals corporate secrets through use of dream-sharing technology, is given the inverse task of planting an idea into the mind of a CEO.",
                   "Language": "English, Japanese, French",
                   "Country": "USA, UK",
                   "Awards": "Won 4 Oscars. Another 143 wins & 198 nominations.",
                   "Poster": "http://ia.media-imdb.com/images/M/MV5BMjAxMzY3NjcxNF5BMl5BanBnXkFtZTcwNTI5OTM0Mw@@._V1_SX300.jpg",
                   "Metascore": "74",
                   "imdbRating": "8.8",
                   "imdbVotes": "1,446,708",
                   "imdbID": "tt1375666",
                   "Type": "movie",
                   "Response": "True"
                },
                {  
                   "Title": "Interstellar",
                   "Year": "2014",
                   "Rated": "PG-13",
                   "Released": "07 Nov 2014",
                   "Runtime": "169 min",
                   "Genre": "Adventure, Drama, Sci-Fi",
                   "Director": "Christopher Nolan",
                   "Writer": "Jonathan Nolan, Christopher Nolan",
                   "Actors": "Ellen Burstyn, Matthew McConaughey, Mackenzie Foy, John Lithgow",
                   "Plot": "A team of explorers travel through a wormhole in space in an attempt to ensure humanity's survival.",
                   "Language": "English",
                   "Country": "USA, UK",
                   "Awards": "Won 1 Oscar. Another 39 wins & 132 nominations.",
                   "Poster": "http://ia.media-imdb.com/images/M/MV5BMjIxNTU4MzY4MF5BMl5BanBnXkFtZTgwMzM4ODI3MjE@._V1_SX300.jpg",
                   "Metascore": "74",
                   "imdbRating": "8.6",
                   "imdbVotes": "910,366",
                   "imdbID": "tt0816692",
                   "Type": "movie",
                   "Response": "True"
                },
                {
                   "Title": "Avatar",
                   "Year": "2009",
                   "Rated": "PG-13",
                   "Released": "18 Dec 2009",
                   "Runtime": "162 min",
                   "Genre": "Action, Adventure, Fantasy",
                   "Director": "James Cameron",
                   "Writer": "James Cameron",
                   "Actors": "Sam Worthington, Zoe Saldana, Sigourney Weaver, Stephen Lang",
                   "Plot": "A paraplegic marine dispatched to the moon Pandora on a unique mission becomes torn between following his orders and protecting the world he feels is his home.",
                   "Language": "English, Spanish",
                   "Country": "USA, UK",
                   "Awards": "Won 3 Oscars. Another 80 wins & 121 nominations.",
                   "Poster": "http://ia.media-imdb.com/images/M/MV5BMTYwOTEwNjAzMl5BMl5BanBnXkFtZTcwODc5MTUwMw@@._V1_SX300.jpg",
                   "Metascore": "83",
                   "imdbRating": "7.9",
                   "imdbVotes": "876,575",
                   "imdbID": "tt0499549",
                   "Type": "movie",
                   "Response": "True"
                }
];

let averageRating;

averageRating = watchList.reduce((a, b) => (parseFloat(a.imdbRating) + parseFloat(b.imdbRating)) /2 );

console.log(averageRating);

I know I have to select only Nolan’s movie but I’m just trying to make an average of all the imdbRatings for now. I was thinking of taking the first value, adding the 2second then dividing the sum by two to make the average of the 2 first ones, then take this value, the accumulator, and start again with the next.
At least that’s how I understand the reduce() function I’m not certain.

This code returns NaN. YET… If I put around it a console.log()

averageRating = watchList.reduce((a, b) => console.log((parseFloat(a.imdbRating) + parseFloat(b.imdbRating)) /2 ));

, it returns the average between the first and second element, and if I add typeof it returns “number”. And as soon as I remove the console.log() around it, the console.log(averageRating); returns NaN

I’m a little lost!

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Link to the challenge:
https://learn.freecodecamp.org/javascript-algorithms-and-data-structures/functional-programming/use-the-reduce-method-to-analyze-data

2

It’s ok I found out I had a bad understanding of the reduce function and the accumulator, everythings works now :slightly_smiling_face:

const nolanMovies = watchList.filter((item) => item.Director === "Christopher Nolan" );

const averageRating = ( nolanMovies.reduce((a, b) => (a + parseFloat(b.imdbRating)),0) ) / nolanMovies.length;

console.log(averageRating);