From: "Florian Aßmann" <florian.assmann@...>
Date: 2007-07-17T00:41:32+09:00
Subject: Re: clean nice way (hash)

Robert Klemme schrieb:
> 2007/7/16, Chris Carter <cdcarter@gmail.com>:
>> On 7/16/07, James Edward Gray II <james@grayproductions.net> wrote:
>> > On Jul 16, 2007, at 5:58 AM, hemant wrote:
>> >
>> > > a.inject({}) {|mem,(key,value)| mem[key] = {'name' => value}; mem }
>> >
>> > I would write that as:
>> >
>> >    a.inject(Hash.new) { |h, (k, v)| h.merge(k => v) }
>> >
>> > James Edward Gray II
>> >
>> >
>>
>> But that doesn't yield what he wanted... You could do
>> a.inject(Hash.new){|h,(k,v)| h.merge(k => { 'name' => value})}
> 
> Still it's inefficient because of all the small Hashes that are thrown
> away immediately. The solution provided by hemant is better although
> not as elegant.
> 
> Kind regards
> 
> robert
> 
> 

Hi,

I also tested a theory of mine, Hash#update does this ~20% faster than
Hash#each:

hash.update(hash) { |key, o_val, n_val| Hash['name' => o_val] }

Thread ID: 101250
Total: 7.24

 %self     total     self     wait    child    calls  name
 66.16      7.24     4.79     0.00     2.45        1  Hash#update
 33.84      2.45     2.45     0.00     0.00   456976  <Class::Hash>#[]
  0.00      7.24     0.00     0.00     7.24        0  Global#[No method]

hash.each { |key, value| hash[key] = Hash['name' => value] }

Thread ID: 101250
Total: 9.28

 %self     total     self     wait    child    calls  name
 60.78      9.28     5.64     0.00     3.64        1  Hash#each
 26.62      2.47     2.47     0.00     0.00   456976  <Class::Hash>#[]
 12.61      1.17     1.17     0.00     0.00   456976  Hash#[]=
  0.00      9.28     0.00     0.00     9.28        0  Global#[No method]

As I profiled both cases I came across something I don't understand:
When I do the profiling of both cases In the same Ruby process the later
one always is slower as when I profile them seperatly, can somebody
explain this?

Regards
Florian

profile_update.rb:
==================
require 'rubygems'
require 'ruby-prof'

puts 'Hash#update'

hash = ('aaaa'..'zzzz').inject Hash.new do |hash, value|
  hash[value] = value
  hash
end

result = RubyProf.profile do
  hash.update(hash) { |key, o_val, n_val| Hash['name' => o_val] }
end
RubyProf::FlatPrinter.new(result).print(STDOUT, 0)


profile_update_first.rb:
========================
require 'rubygems'
require 'ruby-prof'

puts 'Hash#update'

hash = ('aaaa'..'zzzz').inject Hash.new do |hash, value|
  hash[value] = value
  hash
end

result = RubyProf.profile do
  hash.update(hash) { |key, o_val, n_val| Hash['name' => o_val] }
end
RubyProf::FlatPrinter.new(result).print(STDOUT, 0)

puts 'Hash#each'

hash = ('aaaa'..'zzzz').inject Hash.new do |hash, value|
  hash[value] = value
  hash
end

result = RubyProf.profile do
  hash.each { |key, value| hash[key] = Hash['name' => value] }
end
RubyProf::FlatPrinter.new(result).print(STDOUT, 0)


profile_each.rb:
================
require 'rubygems'
require 'ruby-prof'

puts 'Hash#each'

hash = ('aaaa'..'zzzz').inject Hash.new do |hash, value|
  hash[value] = value
  hash
end

result = RubyProf.profile do
  hash.each { |key, value| hash[key] = Hash['name' => value] }
end
RubyProf::FlatPrinter.new(result).print(STDOUT, 0)


profile_each_first.rb:
======================
require 'rubygems'
require 'ruby-prof'

puts 'Hash#each'

hash = ('aaaa'..'zzzz').inject Hash.new do |hash, value|
  hash[value] = value
  hash
end

result = RubyProf.profile do
  hash.each { |key, value| hash[key] = Hash['name' => value] }
end
RubyProf::FlatPrinter.new(result).print(STDOUT, 0)

puts 'Hash#update'

hash = ('aaaa'..'zzzz').inject Hash.new do |hash, value|
  hash[value] = value
  hash
end

result = RubyProf.profile do
  hash.update(hash) { |key, o_val, n_val| Hash['name' => o_val] }
end
RubyProf::FlatPrinter.new(result).print(STDOUT, 0)