01_get_indexes_benchmark.rb

require "benchmark/ips"

NUM_WORDS = 10_000
file = File.open("/usr/share/dict/words")

# Get all the "bo" words
WORDS = file.each_line.grep(/^bo/).map(&:chomp)
file.rewind

puts "#{WORDS.size} \"bo\" words"

# Get non-"bo" words randomly until we have 10,000
file.each_line do |line|
  break if WORDS.size == NUM_WORDS
  next if line.start_with?("bo")
  next if rand > 0.05
  WORDS << line.chomp
end

puts "#{WORDS.size} words total"

def jordan(words)
  words.each_index.select {|idx| words[idx].start_with?("bo") }
end

def mudasobwa(words)
   words.each_with_index
    .grep(->(e) { e.first.start_with? "bo" })
    .map(&:last)
end

def ndn(words)
  words.map.with_index.select {|element, _| element.start_with? 'bo' }.map(&:last)
end

def scott_bartell(words)
  words.map.with_index {|element, index| index if element.start_with? 'bo' }.compact
end

Benchmark.ips do |x|
  x.report("Jordan") { jordan(WORDS) }
  x.report("mudasobwa") { mudasobwa(WORDS) }
  x.report("ndn") { ndn(WORDS) }
  x.report("Scott Bartell") { scott_bartell(WORDS) }
  x.compare!
end

02_result.txt

$ ruby -v
ruby 2.3.1p112 (2016-04-26 revision 54768) [x86_64-darwin15]

$ ruby /tmp/indexes.rb
1122 "bo" words
10000 words total
Warming up --------------------------------------
              Jordan    69.000  i/100ms
           mudasobwa    38.000  i/100ms
                 ndn    43.000  i/100ms
       Scott Bartell    62.000  i/100ms
Calculating -------------------------------------
              Jordan    707.374  (± 3.7%) i/s -      3.588k in   5.079785s
           mudasobwa    385.379  (± 2.6%) i/s -      1.938k in   5.032402s
                 ndn    437.519  (± 3.4%) i/s -      2.193k in   5.018273s
       Scott Bartell    620.111  (± 3.7%) i/s -      3.100k in   5.005881s

Comparison:
              Jordan:      707.4 i/s
       Scott Bartell:      620.1 i/s - 1.14x  slower
                 ndn:      437.5 i/s - 1.62x  slower
           mudasobwa:      385.4 i/s - 1.84x  slower

Woohoo! Only 1.14x slower 😄