An implementation of the SVD recommender used as an example in Ilya Grigorik's blog post "SVD Recommendation System in Ruby" using Ruby-SVD instead of linalg (http://www.igvita.com/2007/01/15/svd-recommendation-system-in-ruby/)

svd-recommender.rb

require 'ruby-svd'

users = { 1 => "Ben", 2 => "Tom", 3 => "John", 4 => "Fred" }

m = SVDMatrix.new(6,4)
ratings = [
  #Ben, Tom, John, Fred
  [5,5,0,5], # season 1
  [5,0,3,4], # season 2
  [3,4,0,3], # season 3
  [0,0,5,3], # season 4
  [5,4,4,5], # season 5
  [5,4,5,5]  # season 6
  ]

ratings.each_with_index do |row, i|
  m.set_row(i, row)
end

p m

lsa = LSA.new(m)

bob = [5,5,0,0,0,5] #new user to classify

similarity = lsa.classify_vector(bob)

similar_users = similarity.delete_if {|k, sim| sim < 0.9}.sort{|a| -a[1]}
similar_users.each do |u|
  puts "#{users[u[0] + 1]} (ID:#{u[0] + 1}, Similarity: #{u[1].round(3)})"
end


similar_user_items = m.column(similar_users[0][0])

not_seen_yet = {}
bob.each_with_index do |r, i|
  not_seen_yet[i] = similar_user_items[i] if bob[i] == 0 && similar_user_items[i] != 0
end

puts "\n#{users[similar_users[0][0]+1]} recommends:"
not_seen_yet.sort_by {|k, v| -v}.each do |k, v|
  puts "\tSeason #{k + 1} .. I gave it a rating of #{v}"
end