From: Ara.T.Howard@...
Date: 2004-11-10T05:23:39+09:00
Subject: Re: Iterating trough hash

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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