From: Michael DeHaan <michael.dehaan@...>
Date: 2004-11-10T06:34:58+09:00
Subject: Re: Iterating trough hash

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
> --
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