Run-length encoding

rle.rb

def rle_regexp(s)
  s.scan(/(.)(\1*)/).map {|c, extra| [c, extra.size+1] }
end

def rle_each_char(s)
  result = []

  last = nil
  count = 0

  s.each_char do |c|
    if c != last and last != nil
      result << [last, count]
      count = 0
    end
    last = c
    count += 1
  end

  result << [last, count] if count > 0

  result
end

def rle_each_cons(s)
  result = []
  count  = 0

  (s.chars + [nil]).each_cons(2) do |a,b|
    count += 1

    if a != b
      result << [a, count]
      count = 0
    end
  end

  result
end

#################################################################################

require 'epitools'

benchmarks = {
  "Very repeated string" => "a"*50000 + "b"*20000 + "c"*9000,
  "No repeats"           => "abc"*50000
}

benchmarks.each do |name, str|
  puts "##### #{name} ##################################"

  bench(
    10,
    rle_regexp: proc { rle_regexp(str) },
    rle_each_char: proc { rle_each_char(str) },
    rle_each_cons: proc { rle_each_cons(str) }
  )
end

zz_output.txt

##### Very repeated string ##################################
                    user     system      total        real
rle_regexp      0.020000   0.000000   0.020000 (  0.029349)
rle_each_char   0.190000   0.000000   0.190000 (  0.193324)
rle_each_cons   0.370000   0.010000   0.380000 (  0.373018)

##### No repeats ##################################
                    user     system      total        real
rle_regexp      1.410000   0.000000   1.410000 (  1.420607)
rle_each_char   1.050000   0.000000   1.050000 (  1.074731)
rle_each_cons   0.890000   0.010000   0.900000 (  0.905797)