http://snippets.dzone.com/posts Fri, 29 Aug 2008 12:35:13 GMT DZone Snippets: average code http://snippets.dzone.com/posts/show/4613 Weighted mean ( http://en.wikipedia.org/wiki/Mean#Weighted_arithmetic_mean ) <br /> <br /><code> <br />class Array <br /> #sum (and mean) found on http://snippets.dzone.com/posts/show/2161 <br /> def sum <br /> inject( nil ) { |sum,x| sum ? sum + x.to_f : x.to_f } <br /> end <br /> <br /> def mean <br /> sum.to_f / size <br /> end <br /> <br /> #http://en.wikipedia.org/wiki/Mean#Weighted_arithmetic_mean <br /> def weighted_mean(weights_array) <br /> raise "Each element of the array must have an accompanying weight. Array length = #{self.size} versus Weights length = #{weights_array.size}" if weights_array.size != self.size <br /> w_sum = weights_array.sum <br /> w_prod = 0 <br /> self.each_index {|i| w_prod += self[i] * weights_array[i].to_f} <br /> w_prod.to_f / w_sum.to_f <br /> end <br />end <br /></code> <br /> <br />Example <br /><code> <br />>> a = [1,2,3] <br />=> [1, 2, 3] <br />>> w = [1,1,1] <br />=> [1, 1, 1] <br />>> a.weighted_arithmetic_mean(w) <br />=> 2.0 <br />>> a.mean <br />=> 2.0 <br />>> w = [5,2,1] <br />=> [5, 2, 1] <br />>> a.weighted_arithmetic_mean(w) <br />=> 1.5 <br /></code> Wed, 03 Oct 2007 21:29:12 GMT http://snippets.dzone.com/posts/show/4613 wiseleyb (ben)