Finding the average of an array using JS [duplicate]

Answer 1

With ES6 you can turn Andy's solution into as a one-liner:

let average = (array) => array.reduce((a, b) => a + b) / array.length;
console.log(average([1,2,3,4,5]));

Answer 2

var total = 0
grades.forEach(function (grade) {
    total += grade        
});
console.log(total / grades.length)

Answer 3

Writing the function for average yourself is crazy. That's why modules exist. I found math.js

In my HTML file:

  <script src="http://cdnjs.cloudflare.com/ajax/libs/mathjs/3.2.1/math.min.js"></script>

(or you can download it)

In my JS code:

math.mean([1,2,3]) // =2
math.mean(1,2,3) // the same
math.mean(grades)

Answer 4

answer to your 1. question:

for ( var i = 0; i < grades.length; i ++){
    var avg = (grades[i] / grades.length) * grades.length
}

avg is declared in each loop. Thus, at the end of the loop, avg has the value of the last item in the array : 68 *5 / 5

Answer 5

There's no built in function, but you can use this to get the sum,

Array.prototype.sum = function() {
    return this.reduce(function(a,b){return a+b;});
};

then divide by the arrays length, e.g.:

var arr = [1,2,3,4,5]
console.log(arr.sum() / arr.length)

Answer 6

It can simply be done with a single reduce operation as follows;

var avg = [1,2,3,4].reduce((p,c,_,a) => p + c/a.length,0);
console.log(avg)