Custom sorting in JavaScript homework question

Question

Write a function named sort_by_average_rating that takes a list/array of key-value stores as a parameter where each key-value store has keys ratings, budget, and box_office where budget and box_office are integers and ratings is a list of integers. Sort the input based on the average of the values in ratings.

I tried adding everything within a for loop when the key is equal to ["ratings"] then after that, I average the results from the two for loops. Lastly, I used a separate function to sort everything.

function key(a,b){
  for(var i = 0; i < a.length; i++){
    tol1 += a[i]["ratings"];  

  for(var x = 0; x < b.length; x++) {
    tol2 += b[x]["ratings"];
    }
    var average = (tol1/tol2);
  }
  return average;
}

function key(x,y){
  if (x[key] < x[key]) { return -1; }
  if (y[key] > y[key]) { return 1; }
  return 0;
 }

function sort_by_average_rating(b){
  b.sort(key)
 }

Result:

[
    {'box_office': 12574015, 'budget': 3986053.18, 'ratings': [8, 7, 1]}, 
    {'box_office': 44855251, 'budget': 3301717.62, 'ratings': [7, 1, 1]}, 
    {'box_office': 36625133, 'budget': 8678591, 'ratings': [7, 6, 2, 8]}, 
    {'box_office': 48397691, 'budget': 15916122.88, 'ratings': [7, 3, 8, 8, 6, 8]}, 
    {'box_office': 43344800, 'budget': 4373679.25, 'ratings': [1, 1, 7, 4]}
]

Expected:

[
    {'box_office': 44855251, 'budget': 3301717.62, 'ratings': [7, 1, 1]}, 
    {'box_office': 43344800, 'budget': 4373679.25, 'ratings': [1, 1, 7, 4]}, 
    {'box_office': 12574015, 'budget': 3986053.18, 'ratings': [8, 7, 1]}, 
    {'box_office': 36625133, 'budget': 8678591.0, 'ratings': [7, 6, 2, 8]}, 
    {'box_office': 48397691, 'budget': 15916122.88, 'ratings': [7, 3, 8, 8, 6, 8]}
]

You have two function key(). Only the second definition is used, the first one is overwritten. Actually, that's just the tip of the iceberg... key inside the function is still referring to the function itself. — Patrick Roberts
– Patrick Roberts, Commented Apr 23, 2019 at 18:21

Shidersz · Accepted Answer · 2019-04-23 18:38:30Z

3

One possible solution is to create a function that return the average of a ratings array, we going to use Array.reduce() for this one. Then you can use this new function with the built-in Array.sort() to generate your desired result:

const input = [
  {'box_office': 12574015, 'budget': 3986053.18, 'ratings': [8, 7, 1]},
  {'box_office': 44855251, 'budget': 3301717.62, 'ratings': [7, 1, 1]},
  {'box_office': 36625133, 'budget': 8678591, 'ratings': [7, 6, 2, 8]},
  {'box_office': 48397691, 'budget': 15916122.88, 'ratings': [7, 3, 8, 8, 6, 8]},
  {'box_office': 43344800, 'budget': 4373679.25, 'ratings': [1, 1, 7, 4]}
];

const getAverage = (arr) =>
{
    return (Array.isArray(arr) && arr.length > 0) ?
           arr.reduce((acc, n) => acc + n) / arr.length :
           0;
};

input.sort((a, b) => getAverage(a.ratings) - getAverage(b.ratings));
console.log(input);

.as-console {background-color:black !important; color:lime;}
.as-console-wrapper {max-height:100% !important; top:0;}

To avoid mutation of the original data, use:

let sorted = input.slice().sort((a, b) => getAverage(a.ratings) - getAverage(b.ratings));

edited Apr 23, 2019 at 18:38

answered Apr 23, 2019 at 18:22

Shidersz

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2 Comments

Patrick Roberts Over a year ago

Would help to pass an initial value of 0 to reduce() in case there are no ratings... though then the result would be NaN. 0/0 is indeterminate.

Shidersz Over a year ago

@PatrickRoberts Thanks for the feedback, I have updated the code.

Nina Scholz · Accepted Answer · 2019-04-23 18:35:37Z

I suggest to use a different approach (sorting with map) by taking the averages in an array and another array for the indices, sort the indices array and map the objects by taking the indices.

const add = (a, b) => a + b;

var array = [{ box_office: 12574015, budget: 3986053.18, ratings: [8, 7, 1] }, { box_office: 44855251, budget: 3301717.62, ratings: [7, 1, 1] }, { box_office: 36625133, budget: 8678591, ratings: [7, 6, 2, 8] }, { box_office: 48397691, budget: 15916122.88, ratings: [7, 3, 8, 8, 6, 8] }, { box_office: 43344800, budget: 4373679.25, ratings: [1, 1, 7, 4] }],
    averages = array.map(({ ratings }) => ratings.reduce(add, 0) / ratings.length),
    indices = [...averages.keys()].sort((i, j) => averages[i] - averages[j]),
    result = indices.map(i => array[i]);
    
console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

junvar · Accepted Answer · 2019-04-23 18:24:32Z

1) you should initialize your variables before using them (e.g. tol1

2) you should avoid repeating function names (e.g. key)

3) you should name your variables and functions something meaningful (e.g. 'a', 'b', 'key', 'x', 'y') mean nothing.

let movies = [
  {'box_office': 12574015, 'budget': 3986053.18, 'ratings': [8, 7, 1]},
  {'box_office': 44855251, 'budget': 3301717.62, 'ratings': [7, 1, 1]},
  {'box_office': 36625133, 'budget': 8678591, 'ratings': [7, 6, 2, 8]},
  {'box_office': 48397691, 'budget': 15916122.88, 'ratings': [7, 3, 8, 8, 6, 8]},
  {'box_office': 43344800, 'budget': 4373679.25, 'ratings': [1, 1, 7, 4]}
];

let averageRating = movie => 
    movie.ratings.reduce((rating, sum) => rating + sum, 0) / movie.ratings.length;

let sortedMovies = movies.sort((movie1, movie2) => averageRating(movie1) - averageRating(movie2));

console.log(sortedMovies);

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