bm.rb

require 'benchmark'

hsh = {}
1000.times {|i| hsh[i.to_s] = i.succ.to_s}

Benchmark.bm do |x|
  x.report("Hash[]") {1000.times{Hash[hsh.values.zip(hsh.keys)]}}
  x.report("invert") {1000.times{hsh.invert}}
  x.report("each_with_object") {1000.times{hsh.each_with_object({}){|(k,v),h| h[v] = k}}}
end

require 'ruby-prof'
require 'fileutils'
# memory, allocations are supposedly to work with patched ruby, but somehow don't
# rvm install 2.1.5 --patch railsexpress -n railsexpress
{
"RubyProf::PROCESS_TIME" => RubyProf::PROCESS_TIME,
"RubyProf::WALL_TIME" => RubyProf::WALL_TIME,
"RubyProf::CPU_TIME" => RubyProf::CPU_TIME,
"RubyProf::ALLOCATIONS" => RubyProf::ALLOCATIONS,
"RubyProf::MEMORY" => RubyProf::MEMORY,
"RubyProf::GC_RUNS" => RubyProf::GC_RUNS,
"RubyProf::GC_TIME" => RubyProf::GC_TIME,
"RubyProf::ALLOCATIONS" => RubyProf::ALLOCATIONS}.each do |mode_name, mode|
  RubyProf.measure_mode = mode
  results = {}
  results["hash_square"] = RubyProf.profile do
    1000.times{Hash[hsh.values.zip(hsh.keys)]}
  end

  results["invert"] = RubyProf.profile do
    1000.times{hsh.invert}
  end

  results["each_with_object"] = RubyProf.profile do
    1000.times{hsh.each_with_object({}){|(k,v),h| h[v] = k}}
  end

  results.each do |name, result|
    FileUtils.mkdir_p("output/#{name}")
    printer = RubyProf::MultiPrinter.new result
    printer.print path: "output/#{name}", profile: mode_name.to_s.downcase.gsub("::", "_")
  end

end

results

       user     system      total        real
Hash[]  0.270000   0.000000   0.270000 (  0.269190)
invert  0.200000   0.000000   0.200000 (  0.197517)
each_with_object  0.340000   0.000000   0.340000 (  0.340221)