Using underscore.js, return the average value from an array of Numbers.

average.js

function average (arr)
{
	return _.reduce(arr, function(memo, num)
	{
		return memo + num;
	}, 0) / arr.length;
}

Hey Jamie, it doesn't work for 0 length arrays. So a slight amendment! :)

     return _.reduce(arr, function(memo, num) {
        return memo + num;
    }, 0) / (arr.length === 0 ? 1 : arr.length);

Infinity and 0 are both wrong for the average of nothing, although Infinity is probably less wrong. Throwing an exception or using an option monad is a better approach.

['3.00', '3.50', '3.33', '2.90']
i need an average of this array please

@Luks1: It's 2.75

@klarstrup LOL

@klarstrup LOL

@klarstrup LOL

_.reduce(
  prices,
  (memo, num) => memo + num,
  0
) / prices.length || 1

or without underscore/lodash

prices.reduce(
  (memo, num) => memo + num,
  0
) / prices.length || 1

or as a one-liner

prices.reduce((memo, num) => memo + num, 0) / prices.length || 1

or as a prototype of array

Array.prototype.avg = function () { return this.reduce((memo, num) => memo + num, 0) / this.length || 1 };

// and then doing prices.avg() which returns the result