results.txt

$ ruby -v
ruby 2.2.3p173 (2015-08-18 revision 51636) [x86_64-darwin14]

Rehearsal --------------------------------------------------------------
map_compact                  0.020000   0.000000   0.020000 (  0.015315)
map_inplace_compact          0.010000   0.000000   0.010000 (  0.016069)
reject_map                   0.010000   0.000000   0.010000 (  0.014038)
reject_inplace_map           0.860000   0.010000   0.870000 (  0.860999)
reject_map_inplace           0.010000   0.000000   0.010000 (  0.013710)
reject_inplace_map_inplace   0.860000   0.000000   0.860000 (  0.866945)
----------------------------------------------------- total: 1.780000sec

                                 user     system      total        real
map_compact                  0.010000   0.000000   0.010000 (  0.012554)
map_inplace_compact          0.010000   0.000000   0.010000 (  0.012114)
reject_map                   0.010000   0.000000   0.010000 (  0.021661)
reject_inplace_map           0.850000   0.000000   0.850000 (  0.855091)
reject_map_inplace           0.010000   0.000000   0.010000 (  0.015349)
reject_inplace_map_inplace   0.870000   0.000000   0.870000 (  0.876531)

test.rb

#!/usr/bin/env ruby

require 'benchmark'

def data
  (0...100_000).to_a
end

def map_compact
  data.map do |i|
    next if i.odd?
    i + i
  end.compact
end

def map_inplace_compact
  data.map! do |i|
    next if i.odd?
    i + i
  end.compact
end

def reject_map
  data.reject { |i| i.odd? }.map { |i| i + i }
end

def reject_inplace_map
  data.reject! { |i| i.odd? }.map { |i| i + i }
end

def reject_inplace_map_inplace
  data.reject! { |i| i.odd? }.map! { |i| i + i }
end

def reject_map_inplace
  data.reject { |i| i.odd? }.map! { |i| i + i }
end

Benchmark.bmbm do |x|
   x.report("map_compact") { map_compact }
   x.report("map_inplace_compact")  { map_inplace_compact }
   x.report("reject_map") { reject_map }
   x.report("reject_inplace_map") { reject_inplace_map }
   x.report("reject_map_inplace") { reject_map_inplace }
   x.report("reject_inplace_map_inplace") { reject_inplace_map_inplace }
end

Fixed in ruby/ruby@5ec029d