Performance of array-averaging in Ruby vs. C

benchmark.rb

require 'benchmark'
require 'extension_cord'

def average_reduce(arr)
  arr.reduce(:+).to_f / arr.size
end

def average_upto(arr)
  sum = 0

  0.upto(arr.size - 1) do |n|
    sum += arr.at(n)
  end

  sum.to_f / arr.size
end

def average_each(arr)
  sum = 0

  arr.each do |val|
    sum += val
  end

  sum.to_f / arr.size
end

def average_while(arr)
  sum = 0
  i = 0

  while i < arr.size
    sum += arr.at(i)
    i += 1
  end

  sum.to_f / arr.size
end

array = Array.new(1_000_000) { rand(0..1000) }

ITERATIONS = 100

Benchmark.bm(10) do |b|
  b.report("reduce:") { ITERATIONS.times { average_reduce(array)             } }
  b.report("upto:")   { ITERATIONS.times { average_upto(array)               } }
  b.report("each:")   { ITERATIONS.times { average_each(array)               } }
  b.report("while:")  { ITERATIONS.times { average_while(array)              } }
  b.report("c:")      { ITERATIONS.times { ExtensionCord.avg_of_array(array) } }
end

# Output:
#                  user     system      total        real
# reduce:      5.900000   0.010000   5.910000 (  5.906489)
# upto:        7.980000   0.000000   7.980000 (  7.994691)
# each:        5.920000   0.010000   5.930000 (  5.929237)
# while:       5.660000   0.000000   5.660000 (  5.661042)
# c:           0.940000   0.000000   0.940000 (  0.943013)