unique calculation using redis

app.rb

require 'sinatra'
require 'redis'
require 'json'
require 'date'

class String

  def &(str)
    result = ''
    result.force_encoding("BINARY")
    min = [self.length, str.length].min
    (0...min).each do |i|
      result << (self[i].ord & str[i].ord)
    end

    result
  end

  def |(str)
    result = ''
    result.force_encoding("BINARY")
    min = [self.length, str.length].min
    (0...min).each do |i|
      result << (self[i].ord | str[i].ord)
    end

    if self.length > str.length
      result << self[min ... self.length]
    elsif self.length < str.length
      result << str[min ... str.length]
    end

    result
  end


  def population_count
    count = 0
    (0 ... self.length).each do |i|
      count += _population_count_byte(self[i].ord)
    end
    count
  end

  private
  ONE_BITS = [0,1,1,2,1,2,2,3,1,2,2,3,2,3,3,4]

  #It works with 8 bits
  def _population_count_byte(x)
    count = 0
    count = ONE_BITS[x&0x0f]
    count += ONE_BITS[x>>4]
    count
  end
end

helpers do
  def redis
    $redis ||= Redis.new
  end

  def unique_count(event, from, to)
    uniques = ''
    (from..to).each do |date|
      key = "#{event}.#{date.strftime('%y%m%d')}"
      bitmap = redis.get(key)
      if bitmap
        bitmap.force_encoding("BINARY")
        uniques |= bitmap
      end
    end
    uniques.population_count
  end

end

get '/collect/:event/for/:user_id/on/:date' do |event,user_id,date|
  time = Date.parse(date)
  key = "#{event}.#{time.strftime('%y%m%d')}"
  if redis.setbit(key, user_id, 1)
    204
  else
    500
  end
end

get '/unique/:event/in/last/:n/days?' do |event,n|
  content_type :json
  to = Date.today
  from = to - n.to_i
  {:from => from, :to => to, :unique_count => unique_count(event,from,to)}.to_json
end

http://blog.getspool.com/2011/11/29/fast-easy-realtime-metrics-using-redis-bitmaps/