Now featuring results

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

Results

Rehearsal ------------------------------------------------
map, compact   1.090000   0.040000   1.130000 (  2.573331)
inject        19.150000   0.370000  19.520000 ( 34.193527)
accumulator   11.760000   0.220000  11.980000 ( 16.703419)
map, reject    1.740000   0.040000   1.780000 (  2.365760)
-------------------------------------- total: 34.410000sec

                   user     system      total        real
map, compact   1.080000   0.030000   1.110000 (  1.440510)
inject        12.800000   0.230000  13.030000 ( 17.273436)
accumulator    6.270000   0.120000   6.390000 (  8.737844)
map, reject    1.640000   0.050000   1.690000 (  2.296689)