gistfile1.txt

def sim_dist items, user1, user2
  keys = items.to_a.map{|x| x[1].keys}.flatten.uniq
  sum = keys.map{ |item|
    if items[user1][item] == nil or items[user2][item] == nil
      0
    else
      Math.sqrt((items[user1][item] - items[user2][item]) ** 2)
    end
  }.reduce(0){|r, x| r + x}
  1 / (sum +1)
end

def sim_user items, user
   users = items.to_a.map{|x| x[0]}.find_all{|u| u != user}
   users.map{|u| [u,sim_dist(items, user, u)]}
        .sort{|x,y| y[1] - x[1]}
        .first[0]
end

def recom_item items, user
   users = items.to_a.map{|x| x[0]}.find_all{|u| u != user}
   items2 = users.map{|u|
     [u, items[u].reject{|x| items[user].map{|x| x[0]}.index(x) }
                 .map{|x| [x[0], x[1] * sim_dist(items, user, u)]}]}

   table = items2.map{|x| x[1]}
                 .flatten(1)
                 .reduce({}){|r, xs|
                      k = xs[0]
                      v = xs[1]
                      r[k] = (r[k] == nil) ? v : r[k] + v
                      r
                 }

   table.to_a.sort{|x, y| y[1] - x[1]}.first[0]
end

items= {
        :Taro    =>{:A=>2.5, :B=>3.5, :C=>2},
        :Hanako  =>{:A=>2.3, :B=>3.5, :C=>2.1, :D=>4},
        :Sanshiro=>{:A=>1.5, :B=>3.5, :C=>2, :E=>1},
        :Goro    =>{:A=>1.5, :B=>3.5, :C=>2, :E=>4}
}

sim_dist(items, :Taro, :Sanshiro)