How to compute the sum and average of elements in

Question

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I am having problems adding all the elements of an array as well as averaging them out. How would I do this and implement it with the code I currently have? The elements are supposed to be defined as I have it below.

<script type="text/javascript">
//<![CDATA[

var i;
var elmt = new Array();

elmt[0] = "0";
elmt[1] = "1";
elmt[2] = "2";
elmt[3] = "3";
elmt[4] = "4";
elmt[5] = "7";
elmt[6] = "8";
elmt[7] = "9";
elmt[8] = "10";
elmt[9] = "11";

// Problem here
for (i = 9; i < 10; i++){
  document.write("The sum of all the elements is: " + /* Problem here */ + " The average of all the elements is: " + /* Problem here */ + "<br/>");
}   

//]]>
</script>

Answer 1

I use these methods in my personal library:

Array.prototype.sum = Array.prototype.sum || function() {
  return this.reduce(function(sum, a) { return sum + Number(a) }, 0);
}

Array.prototype.average = Array.prototype.average || function() {
  return this.sum() / (this.length || 1);
}

EDIT: To use them, simply ask the array for its sum or average, like:

[1,2,3].sum() // = 6
[1,2,3].average() // = 2

Answer 2

If anyone ever needs it - Here is a recursive average.

In the context of the original question, you may want to use the recursive average if you allowed the user to insert additional values and, without incurring the cost of visiting each element again, wanted to "update" the existing average.

/**
 * Computes the recursive average of an indefinite set
 * @param {Iterable<number>} set iterable sequence to average
 * @param {number} initAvg initial average value
 * @param {number} initCount initial average count
 */
function average(set, initAvg, initCount) {
  if (!set || !set[Symbol.iterator])
    throw Error("must pass an iterable sequence");

  let avg = initAvg || 0;
  let avgCnt = initCount || 0;
  for (let x of set) {
    avgCnt += 1;
    avg = avg * ((avgCnt - 1) / avgCnt) + x / avgCnt;
  }
  return avg; // or {avg: avg, count: avgCnt};
}

average([2, 4, 6]);    //returns 4
average([4, 6], 2, 1); //returns 4
average([6], 3, 2);    //returns 4
average({
  *[Symbol.iterator]() {
    yield 2; yield 4; yield 6;
  }
});                    //returns 4

How:

this works by maintaining the current average and element count. When a new value is to be included you increment count by 1, scale the existing average by (count-1) / count, and add newValue / count to the average.

Benefits:

• you don't sum all the elements, which may result in large number that cannot be stored in a 64-bit float.
• you can "update" an existing average if additional values become available.
• you can perform a rolling average without knowing the sequence length.

Downsides:

• incurs lots more divisions
• not infinite - limited to Number.MAX_SAFE_INTEGER items unless you employ BigNumber

Answer 3

I think we can do like

var k=elmt.reduce(function(a,b){return parseFloat(a+parseFloat(b));})
var avg=k/elmt.length; 
console.log(avg);

I am using parseFloat twice because when 1) you add (a)9+b("1") number then result will be "91" but we want addition. so i used parseFloat

2)When addition of (a)9+parseFloat("1") happen though result will be "10" but it will be in string which we don't want so again i used parseFloat.

I hope i am clear. Suggestions are welcome

Answer 4

I think this may be a direct solution to calculate the average with a for loop and function.

var elmts = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11];

function average(arr) {
    var total = 0;
    for (var i = 0; i < arr.length; i++) {
        total += arr[i];
    }
        console.log(Math.round(total/arr.length));
}

average(elmts);

Answer 5

Calculating average (mean) using reduce and ES6:

const average = list => list.reduce((prev, curr) => prev + curr) / list.length;

const list = [0, 10, 20, 30]
average(list) // 15

Answer 6

here's your one liner:

var average = arr.reduce((sum,item,index,arr)=>index !== arr.length-1?sum+item:sum+item/arr.length,0)