# How to compute the average rating? : Use the reduce Method to Analyze Data [SOLVED]

How to compute the average rating? : Use the reduce Method to Analyze Data [SOLVED]
0

#1

The average rating I get is 8.52 whereas FCC’s averageRating should equal 8.675.
If I’m not mistaken, to compute an average of something is to add up all the numbers, then divide by how many numbers there are. In other words it is the sum divided by the count.

``````// the global variable
var watchList = [
{
"Title": "Inception",
"Year": "2010",
"Rated": "PG-13",
"Released": "16 Jul 2010",
"Runtime": "148 min",
"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/[email protected]@._V1_SX300.jpg",
"Metascore": "74",
"imdbRating": "8.8",
"imdbID": "tt1375666",
"Type": "movie",
"Response": "True"
},
{
"Title": "Interstellar",
"Year": "2014",
"Rated": "PG-13",
"Released": "07 Nov 2014",
"Runtime": "169 min",
"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/[email protected]_V1_SX300.jpg",
"Metascore": "74",
"imdbRating": "8.6",
"imdbID": "tt0816692",
"Type": "movie",
"Response": "True"
},
{
"Title": "The Dark Knight",
"Year": "2008",
"Rated": "PG-13",
"Released": "18 Jul 2008",
"Runtime": "152 min",
"Director": "Christopher Nolan",
"Writer": "Jonathan Nolan (screenplay), Christopher Nolan (screenplay), Christopher Nolan (story), David S. Goyer (story), Bob Kane (characters)",
"Actors": "Christian Bale, Heath Ledger, Aaron Eckhart, Michael Caine",
"Plot": "When the menace known as the Joker wreaks havoc and chaos on the people of Gotham, the caped crusader must come to terms with one of the greatest psychological tests of his ability to fight injustice.",
"Language": "English, Mandarin",
"Country": "USA, UK",
"Awards": "Won 2 Oscars. Another 146 wins & 142 nominations.",
"Poster": "http://ia.media-imdb.com/images/M/[email protected]@._V1_SX300.jpg",
"Metascore": "82",
"imdbRating": "9.0",
"imdbID": "tt0468569",
"Type": "movie",
"Response": "True"
},
{
"Title": "Batman Begins",
"Year": "2005",
"Rated": "PG-13",
"Released": "15 Jun 2005",
"Runtime": "140 min",
"Director": "Christopher Nolan",
"Writer": "Bob Kane (characters), David S. Goyer (story), Christopher Nolan (screenplay), David S. Goyer (screenplay)",
"Actors": "Christian Bale, Michael Caine, Liam Neeson, Katie Holmes",
"Plot": "After training with his mentor, Batman begins his fight to free crime-ridden Gotham City from the corruption that Scarecrow and the League of Shadows have cast upon it.",
"Language": "English, Urdu, Mandarin",
"Country": "USA, UK",
"Awards": "Nominated for 1 Oscar. Another 15 wins & 66 nominations.",
"Poster": "http://ia.media-imdb.com/images/M/MV5BNTM3OTc0MzM2OV5BMl5BanBnXkFtZTYwNzUwMTI3._V1_SX300.jpg",
"Metascore": "70",
"imdbRating": "8.3",
"imdbID": "tt0372784",
"Type": "movie",
"Response": "True"
},
{
"Title": "Avatar",
"Year": "2009",
"Rated": "PG-13",
"Released": "18 Dec 2009",
"Runtime": "162 min",
"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/[email protected]@._V1_SX300.jpg",
"Metascore": "83",
"imdbRating": "7.9",
"imdbID": "tt0499549",
"Type": "movie",
"Response": "True"
}
];

let filteredList = watchList.filter((x) => (x.Director = "Cristopher Nolan"))

let mappedList = filteredList.map((x) => ( x.imdbRating));

let numberedList = mappedList.map(Number);

let totalRating = numberedList.reduce((total, rating) => total + rating  )  ;

var averageRating = totalRating / numberedList.length;

console.log(averageRating);
``````

#2

This is a little bit of a sneaky one. The instructions tell you to get the average rating of Nolan’s films. Are all the films in the array Nolan films?

#3

Okay, Avatar is not a Christopher Nolan Film. Thanks

#4

Solved it. Thanks for the heads up. Yeah, its a little sneaky:

``````let filteredList = watchList.filter((x) => (x.Director === "Christopher Nolan"));

let mappedList = filteredList.map((x) => ( x.imdbRating));

let numberedList = mappedList.map(Number);

let totalRating = numberedList.reduce((total, rating) => total + rating  )  ;

var averageRating = totalRating / numberedList.length;

``````

#5

Sure, that works. I might suggest that you don’t need to loop through the array four times. I think it’s more natural do it all with just two loops:

``````let filteredList = watchList.filter(f => f.Director === 'Christopher Nolan')
let averageRating = filteredList.reduce((acc, cur) => acc + +cur.imdbRating, 0
)/filteredList.length
``````

Of course, with a little creativity, you could also do it in one pass:

``````let tot = 0
var averageRating = watchList.reduce((acc, cur) => {
if (cur.Director === 'Christopher Nolan') {
tot++
return acc + +cur.imdbRating
} else {
return acc
}
}, 0)/tot
``````

This last one takes up more lines on the page but would actually be a little faster.

I suppose you could try to put it all in one line:

``````let tot = 0
let averageRating = watchList.reduce((acc, cur) => cur.Director === 'Christopher Nolan' ? ++tot ? acc + +cur.imdbRating : null : acc, 0)/tot
``````

But at some point it gets ridiculous.