Javascript: Calculating the average of an array using for-loop

Question

Like the title suggests, what I need to do is calculating the average of an array using for-loop. And by average I mean (a+b+c+d+e)/5=average.

That's what I need to do in text, since I'm new at javascript I don't quite know how to execute this. Any ideas?

Also, if you think this question doesn't belong here or is stupid, please direct me to somewhere where I can find this information, I'm just trying to learn here.

function test(arr) {


}

see this http://stackoverflow.com/questions/10359907/array-sum-and-average — BEHZAD, Jan 03 '14 at 14:08
Here is a good post [Array Sum and Average][1] [1]: http://stackoverflow.com/questions/10359907/array-sum-and-average — BEHZAD, Jan 03 '14 at 14:11

Panagiotis Panagi · Answer 1 · 2014-01-03T14:49:02.503

5

function average(items) {
  var sum = 0;
  var count = items.length;
  for (i=0; i<count; i++) {
    sum += items[i];
  }
  return sum/count;
}

Or if you want average() to be available as a method on arrays:

Array.prototype.average = function() {
  var sum = 0;
  var count = this.length;
  for (i=0; i<count; i++) {
    sum += this[i];
  }
  return sum/count;
}

Usage:

[1,2,3,4,5].average(); // 3

edited Jan 03 '14 at 14:49

answered Jan 03 '14 at 14:05

Panagiotis Panagi

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@AndrewP Inside the loop, we add the values one-by-one into an accumulator (`average` variable). After the loop we divide the sum with the number of amounts. – Panagiotis Panagi Jan 03 '14 at 14:47

score 1 · Answer 2 · edited May 23 '17 at 11:54

1

Here is a post with the response to your answer.

Array Sum and Average

Also check this link about for loop in Javascript:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for_each...in

edited May 23 '17 at 11:54

Community

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answered Jan 03 '14 at 14:05

Aerilys

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score 1 · Accepted Answer · answered Jan 03 '14 at 14:33

1

Just iterate over the values, sum them up, and return the value of sum, divided by the number of entries.

function test (arr) {
  for (var i=0,sum=0;i<arr.length;i++) {
    sum += arr[i];
  }
  return sum / i;
}

answered Jan 03 '14 at 14:33

Moritz Roessler

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score 0 · Answer 4 · answered Jan 03 '14 at 14:12

0

This should help

var nCtrr = 0, nSum = 0, nAvg = 0;
var arNum = [1, 2, 3, 4, 5];
for ( nCtr in arNum ) {

    nSum += arNum[ nCtr ];
    nCtr += 1;

}
nAvg = nSum/arNum.length;
alert( nAvg );

JSFiddle

answered Jan 03 '14 at 14:12

score 0 · Answer 5 · edited May 23 '17 at 12:34

Suggestion, none of the answers here check for length === 0, you'll be dividing by zero in some situation in the future. I suggest you always check mathematical boundary conditions. The related article had one response which caught that (https://stackoverflow.com/a/18234568/987044).

Here is another example if you want to be safe. http://jsfiddle.net/ledlogic/syn74/

var nothing = null;
var empty = [];
var items = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]; // 20 sider
function average(items) {
    if (!items) {
        return 0;
    }
    var sum = 0,
        count = 0;
    // for large arrays, faster to go down.
    for (var count = items.length, i = count - 1; i >= 0; i--) {
        sum += items[i];
    }
    return count ? sum / count : 0;
}

alert(nothing + ":" + average(nothing) + "\r" + empty + ":" + average(empty) + "\r" + items + ":" + average(items) + "\r");

The math.js library, mean.js also does array length checking.

Javascript: Calculating the average of an array using for-loop

5 Answers5