From: Michael DeHaan <michael.dehaan@...>
Date: 2004-11-10T06:41:08+09:00
Subject: Re: Iterating trough hash

Hmm, that's not a good bug there, so I'll pull the "history" thing out
(I was trying to be too clever)...

module Enumerable
 def each_permutation
   each do |item1|
     each do |item2|
         yield [item1,item2] unless (item1 === item2)
     end
   end
 end
end




On Tue, 9 Nov 2004 16:34:55 -0500, Michael DeHaan
<michael.dehaan@gmail.com> wrote:
> This is a really long one, so (being new to the language), I'd
> appreciate feedback.   Note here we don't print dups, and we also can
> provide a custom definition of whether two people are equal...However
> it doesn't use a hash quite as the OP requested :)
> 
> module Enumerable
>  def each_permutation
>    history = Hash.new()
>    each do |item1|
>      each do |item2|
>          history[item1] = 1
>          yield [item1,item2] unless (item1 === item2 || history.has_key?(item2))
>      end
>    end
>  end
> end
> 
> class Person
>    attr_reader :age
>    attr_reader :name
> 
>    def initialize(name,age)
>       @name=name;
>       @age=age;
>    end
> 
>    def ===(other)
>       return ((@age==other.age())&&(@name==other.name()))
>    end
> 
>    def to_s
>       @name
>    end
> 
> end
> 
> @persons = [
>    Person.new('Timmy',5),
>    Person.new('Jimmy',10),
>    Person.new('Sally',40)
> ]
> 
> @persons.each_permutation do | p1, p2 |
>  puts "#{p1} shakes hands with #{p2}. Together they are
> #{p1.age()+p2.age()} years old."
> end
> 
> On Wed, 10 Nov 2004 05:23:39 +0900, ara.t.howard@noaa.gov
> 
> 
> <ara.t.howard@noaa.gov> wrote:
> > On Wed, 10 Nov 2004, Mark Hubbart wrote:
> >
> >
> >
> > >>    if h.sort.index([person1,h[person1]]) < h.sort.index([person2,h[person2]])
> > >>
> > >> says:
> > >>
> > >>    if the name of person1 is less than the name of person2 OR the names are the
> > >>    SAME but the age of person1 is less than the age of person2.
> > >
> > > Um, no, I think this says:
> > >
> > >  if the index of the first element that matches [person1, age1] is
> > > greater than the
> > >  index of the first element that matches [person2, age2].
> >
> > consider the meaning of the h.sort and how ruby will do it by default.
> >
> >    h.sort       => array of key value pairs sorted first on name then on age
> >
> >    h.sort.index => look for the natural ordering of an entry where the
> >                    ordering has been defined by ruby's Array#sort method
> >
> > you are correct in what you said - but what does that __mean__?  if you think
> > of what would cause an index to be less than the index of another entry you'll
> > see what i mean: a particular key/val pair will only have a lesser index in
> > the array produced by h.sort if either the name in the entry sorts first or
> > the names are the same and the age sorts first.  as you pointed out the names
> > cannot be the same since the data is stored in a hash - so why include age in
> > the search for ordering index when it can never be a tie breaker?  eg this
> > code would have the same effect
> >
> >    if h.keys.sort.index(person1) < h.keys.sort.index(person2)
> >
> > my concern was that the OP included the age in the ordering search thinking it
> > had some effect - it doesn't.  in fact dermining the name's (or name/age pair)
> > index into an ordered list is exactly the same as simply comparing names isn't
> > it:
> >
> >    harp:~ > cat a.rb
> >    h = {"john" => 41, "mary" => 31, "fred" => 10}
> >
> >    puts '---'
> >    h.each_key do |person1|
> >      h.each_key do |person2|
> >
> >        if h.sort.index([person1,h[person1]])<h.sort.index([person2,h[person2]])   # <--
> >
> >          age=(h[person1]+h[person2]).to_s
> >          puts "#{person1} shakes hands with #{person2}. Together they are #{age} years old"
> >        end
> >      end
> >    end
> >
> >    puts '---'
> >    h.each_key do |person1|
> >      h.each_key do |person2|
> >
> >        if person1 < person2                                                        # <--
> >
> >          age=(h[person1]+h[person2]).to_s
> >          puts "#{person1} shakes hands with #{person2}. Together they are #{age} years old"
> >        end
> >      end
> >    end
> >
> >    harp:~ > ruby a.rb
> >    ---
> >    john shakes hands with mary. Together they are 72 years old
> >    fred shakes hands with john. Together they are 51 years old
> >    fred shakes hands with mary. Together they are 41 years old
> >    ---
> >    john shakes hands with mary. Together they are 72 years old
> >    fred shakes hands with john. Together they are 51 years old
> >    fred shakes hands with mary. Together they are 41 years old
> >
> > so - why do you think the OP included age in the search?  what was the code
> > trying to say?
> >
> > kind regards.
> >
> >
> >
> > -a
> > --
> > ===============================================================================
> > | EMAIL   :: Ara [dot] T [dot] Howard [at] noaa [dot] gov
> > | PHONE   :: 303.497.6469
> > | When you do something, you should burn yourself completely, like a good
> > | bonfire, leaving no trace of yourself.  --Shunryu Suzuki
> > ===============================================================================
> >
> >
>