freeCodeCamp Challenge Guide: Use the reduce Method to Analyze Data

Question

I am in the freeCodeCamp Use the reduce Method to Analyze Data challenge.

I tried:

function getRating(watchList){
  // Add your code below this line
  var count = 0;
  var sum = 0;
  var averageRating = watchList.reduce(function (obj)  {
    if (obj.Director === "Christopher Nolan") {
      count++;
      
      sum =  sum + parseFloat(obj.imdbRating);
      
    }
    
    return sum;
  }, 0) / count;
  // Add your code above this line
  return averageRating;
}

The result is NaN, what I am doing wrong? I must use the arrow function, because standard function declaration produced unexpected results?

Thanks for help

Answer 1

I will give you hint.

const res = watchList.filter((d) => d.Director === 'James Cameron').map(x => x.averageRating));

Then another map to Numbers

 res.map(Number)

Now use reduce to calculate average of numbers. Everything is explained here.

Answer 2

you can try:

const relevant = watchList.filter(movie => movie.Director === "Christopher Nolan");
const total = relevant.reduce((sum, movie) => sum + Number(movie.imdbRating), 0);
const average = total / relevant.length;

or combine the last 2 lines:

const relevant = watchList.filter(movie => movie.Director === "Christopher Nolan");
const average = relevant.reduce((sum, movie) => sum + Number(movie.imdbRating), 0) / relevant.length;

Answer 3

function getRating(watchList){
  // Add your code below this line
  var titles = watchList.filter(function(obj){
return obj.Director === "Christopher Nolan";
});
//message(titles);
var averageRating = titles


.reduce( function(sum,obj){
  return sum = sum + parseFloat(obj.imdbRating);
}, 0)/titles.length;
  //message(watchList.Director);
   
  // Add your code above this line
  return averageRating;
}

Answer 4

let averageRating = watchList
.filter(movie => movie.Director === "Christopher Nolan")
.map(movie => Number(movie.imdbRating))
.reduce((sum, movie, index, arr) => ((movie/arr.length)+ sum), 0);