実験でrubyの「普通」な書き方と、関数型っぽい書き方の実行速度を比べてみたくなったので、消費税計算っぽい事をお題にやってみた。

sample.rb

#-*- coding:utf-8 -*-
#
# Ruby skeleton file
#
 
require 'benchmark'
require 'ruby-prof'
 
itrs = 500
 
price = 101
# list = [1000, 2000, 696, 389, 392]
list = []
 
itrs.times do
  list << rand(100)
end
 
# 単純に税込みにするための関数を追加
class Numeric
  def tax
    (self * Base::TAX_RATE).floor
  end
 
  def tax_lambda
    -> i{(self * Base::TAX_RATE).floor}
  end
end
 
class Base
  TAX_RATE = 1.05
 
  def self.tax(price)
    (price * TAX_RATE).floor
  end
 
  def self.sum0(list)
    total = 0
 
    list.each {|l| total += self.tax(l)}
 
    return total
  end
 
  def self.sum0_n(list)
    total = 0
 
    list.each {|l| total += l.tax}
 
    return total
  end
 
  def self.sum_i(list)  
    return 0 if list.empty?
    list.first.tax + Base.sum_i(list.drop 1)
  end
 
  def self.fact(n)
    return 1 if n == 0
    n * self.fact(n - 1)
  end
 
  def self.sum1(list)
    list.inject(0) {|l, m| l + self.tax(m)}
  end
 
  def self.sum2(list)
    list.map(&-> i{self.tax(i)}).reduce(:+)
  end
 
  def self.sum3(list)
    list.map{|i| self.tax(i)}.reduce(:+)
  end
 
  def self.sum4(list)
    list.map{|i| self.tax(i)}.inject(:+)
  end
 
  def self.sum5(list)
    list.lazy.select{|a| a < 50}.map{|i| self.tax(i)}.to_a.reduce(:+)
  end
 
  def self.sum6(list)
    list.lazy.map{|i| self.tax(i)}.to_a.reduce(:+)
  end
 
  def self.time
    st = Time.now
    yield
    tt = Time.now - st
  end
end
 
puts "Base.fact(6) = #{Base.fact(6)}"
puts "Base.sum_i(list) = #{Base.sum_i(list)}"
 
puts "1) Base.tax(price) = #{Base.tax(price)}"
puts "2) Base.sum0(list) = #{Base.sum0(list)}"
puts "3) Base.sum1(list) = #{Base.sum1(list)}"
puts "4) Base.sum2(list) = #{Base.sum2(list)}"
puts "5) Base.sum3(list) = #{Base.sum3(list)}"
puts "6) Base.sum4(list) = #{Base.sum4(list)}"
puts "7) Base.sum5(list) = #{Base.sum5(list)}"
 
 
# res0 = Base.time do
res0 = Benchmark.measure do
  itrs.times do
    100.tax
  end
end
res1 = Benchmark.measure do
  itrs.times do
    100.tax_lambda
  end
end
res2 = Benchmark.measure do
  itrs.times do
    Base.sum0(list)
  end
end
res3 = Benchmark.measure do
  itrs.times do
    Base.sum1(list)
  end
end
res4 = Benchmark.measure do
  itrs.times do
    Base.sum2(list)
  end
end
res5 = Benchmark.measure do
  itrs.times do
    Base.sum3(list)
  end
end
res6 = Benchmark.measure do
  itrs.times do
    Base.sum4(list)
  end
end
res7 = Benchmark.measure do
  itrs.times do
    Base.sum5(list)
  end
end
 
res8 = Benchmark.measure do
  itrs.times do
   Base.sum_i(list)
  end
end
 
#==============================
result = RubyProf.profile do
  itrs.times do
    Base.sum5(list)
  end
end
 
puts 'res1'
# Print a flat profile to text
printer = RubyProf::FlatPrinter.new(result)
printer.print(STDOUT)
 
#==============================
result2 = RubyProf.profile do
  itrs.times do
    Base.sum6(list)
  end
end
 
puts 'res2'
# Print a flat profile to text
printer = RubyProf::FlatPrinter.new(result2)
printer.print(STDOUT)
 
#==============================
result3 = RubyProf.profile do
  itrs.times do
    Base.sum0(list)
  end
end
 
puts 'res3'
# Print a flat profile to text
printer = RubyProf::FlatPrinter.new(result)
printer.print(STDOUT)
 
#==============================
result4 = RubyProf.profile do
  itrs.times do
    Base.sum_i(list)
  end
end
 
puts 'res4'
# Print a flat profile to text
printer = RubyProf::FlatPrinter.new(result2)
printer.print(STDOUT)
 
puts "1) time tax    = #{res0}"
puts "2) time lambda = #{res1}"
puts "3) time sum0   = #{res2}"
puts "4) time sum1   = #{res3}"
puts "5) time sum2   = #{res4}"
puts "6) time sum3   = #{res5}"
puts "7) time sum4   = #{res6}"
puts "8) time sum5   = #{res7}"
puts "9) time sum_i  = #{res8}"

全然まとめられてないんですが、

1. time tax = 0.000000 0.000000 0.000000 ( 0.000110)
2. time lambda = 0.000000 0.000000 0.000000 ( 0.000385)
3. time sum0 = 0.070000 0.000000 0.070000 ( 0.068708)
4. time sum1 = 0.070000 0.000000 0.070000 ( 0.070950)
5. time sum2 = 0.070000 0.010000 0.080000 ( 0.074503)
6. time sum3 = 0.080000 0.000000 0.080000 ( 0.079940)
7. time sum4 = 0.080000 0.000000 0.080000 ( 0.084216)
8. time sum5 = 0.220000 0.000000 0.220000 ( 0.214901)
9. time sum_i = 0.130000 0.000000 0.130000 ( 0.130125)

普通にeach で書くのが一番早かった。そりゃそうか。