comprehend.rb

module Enumerable
  def comprehend(&block)
    map(&block).compact
  end
  
  def comprehend2(&block)
    inject([]){|arr, x| result = block[x]; arr << result if result; arr}
  end
  
  def comprehend3(&block)
    arr = []
    each do |x|
      result = block[x]
      arr << result if result
    end
    arr
  end

  def comprehend4(&block)
    map(&block).reject{|x| x.nil?}
  end
end


require "benchmark"

block = lambda {|x| x * 2 if x > 50 }
arr = (1..100_000).to_a
TESTS = 10
Benchmark.bmbm do |results|
  results.report("map, compact") {TESTS.times{arr.comprehend(&block)}}
  results.report("inject") {TESTS.times{arr.comprehend2(&block)}}
  results.report("accumulator") {TESTS.times{arr.comprehend3(&block)}}
  results.report("map, reject") {TESTS.times{arr.comprehend4(&block)}}
end