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def pearson(first,second) common = first.select{|title,rating| second.include?(title) } return if common.empty? first_sum = common.inject(0){|total,c| total + first[c.first]} second_sum = common.inject(0){|total,c| total + second[c.first]} first_squares = common.inject(0){|total,c| total + first[c.first] ** 2} second_squares = common.inject(0){|total,c| total + second[c.first] ** 2} density = Math.sqrt((first_squares - first_sum ** 2 / common.size)*(second_squares - second_sum ** 2 / common.size)) products = common.inject(0){|total, c| total + (first[c.first] * second[c.first])} return if density.zero? return (products-(first_sum*second_sum/common.size))/density end
Refactorings
No refactoring yet !
Brianthecoder
March 13, 2008, March 13, 2008 15:17, permalink
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Here's a spec
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before(:each) do @critics = { "Lisa Rose" => {"Lady in the Water" => 2.5, "Snakes on a Plane" => 3.5, "Just My Luck" => 3.0, "Superman Returns" => 3.5, "You, Me, and Dupree" => 2.5, "The Night Listener" => 3.0}, "Gene Seymour" => {"Lady in the Water" => 3.0, "Snakes on a Plane" => 3.5, "Just My Luck" => 1.5, "Superman Returns" => 5.0, "You, Me, and Dupree" => 3.5, "The Night Listener" => 3.0}, "Michael Phillips" => {"Lady in the Water" => 2.5, "Snakes on a Plane" => 3.0, "Superman Returns" => 3.5, "The Night Listener" => 4.0}, "Claudia Puig" => {"Snakes on a Plane" => 3.5, "Just My Luck" => 3.0, "Superman Returns" => 4.0, "You, Me, and Dupree" => 2.5, "The Night Listener" => 4.5}, "Mick LaSalle" => {"Lady in the Water" => 3.0, "Snakes on a Plane" => 4.0, "Just My Luck" => 2.0, "Superman Returns" => 3.0, "You, Me, and Dupree" => 2.0, "The Night Listener" => 3.0}, "Jack Matthews" => {"Lady in the Water" => 3.0, "Snakes on a Plane" => 4.0, "Superman Returns" => 5.0, "You, Me, and Dupree" => 3.5, "The Night Listener" => 3.0}, "Toby" => {"Snakes on a Plane" => 4.5, "Superman Returns" => 4.0, "You, Me, and Dupree" => 1.0} } end it "should calculate peason similarity" do pearson(@critics["Lisa Rose"], @critics["Gene Seymour"]).should be_close(0.396059017191, 0.000001) end
This was ported from python, but I know it can be done better.