inject vs plus vs concat

inject_vs_plus.rb

require 'benchmark'

class PerfTest
  def with_inject(array)
    mapped_vals.inject(array, :<<)
  end

  def with_plus(array)
    array + mapped_vals
  end

  def with_each(array)
    mapped_vals.each {|i| array << i }
    array
  end

  def with_concat(array)
    array.concat(mapped_vals)
  end

  private
  def mapped_vals
    (1..1_000_000).map do |i|
      i * i * i * i
    end
  end
end


Benchmark.bmbm(10) do |bm|
  bm.report("with plus") { PerfTest.new.with_plus([1, 2, 3, 4, 5]) }
  bm.report("with concat") { PerfTest.new.with_concat([1, 2, 3, 4, 5]) }
  bm.report("with each") { PerfTest.new.with_each([1, 2, 3, 4, 5]) }
  bm.report("with inject") { PerfTest.new.with_inject([1, 2, 3, 4, 5]) }
end

results

Rehearsal -----------------------------------------------
with plus     0.380000   0.020000   0.400000 (  0.393140)
with concat   0.270000   0.010000   0.280000 (  0.302586)
with each     0.360000   0.010000   0.370000 (  0.397857)
with inject   0.380000   0.000000   0.380000 (  0.421292)
-------------------------------------- total: 1.430000sec

                  user     system      total        real
with plus     0.300000   0.000000   0.300000 (  0.307589)
with concat   0.270000   0.000000   0.270000 (  0.271764)
with each     0.380000   0.000000   0.380000 (  0.419320)
with inject   0.350000   0.010000   0.360000 (  0.388192)