From: Jim Weirich <jim.weirich@...>
Date: 2008-08-06T13:51:58+09:00
Subject: [ruby-core:18140] Re: New array methods cycle, choice, shuffle (plus bug in cycle)


On Aug 5, 2008, at 7:23 PM, Charles Oliver Nutter wrote:

> Brian Candler wrote:
>> If there are no good ideas left, perhaps things should be left as  
>> they are.
>> Or does that make me a heretic?
>
> I find I frequently need to get only the second element of an array,  
> or perhaps the seventh. So perhaps if we have choice/pick/sample  
> then we should implement "second" through "tenth" as well. Maybe  
> also powers of ten beyond that... "tenth", "twentieth", "thirtieth".

Excellent idea.  Below is some code to handle ordinal numbers up to  
nine_hundred_ninety_nine.  Provided as a mixin so you can mix it into  
array, or into any other class that implements the [] method.  I think  
the use case for ordinals beyond 999 is rare enough that we don't have  
to include them in the standard library.

> Maybe also every_other, every_third, every_fourth so I can dice my  
> arrays without wearing _why's flip-flops.

No, I think you are wildly off base with this suggestion.  However, I  
am considering proposing a version of Lisp's cxxxr functions (e.g.  
cadr, caddr) to navigate arbitrarily nested array structures.

-- 
-- Jim Weirich
-- jim.weirich@gmail.com

Code below:

module Ordinal
   class OrdinalNameError < RuntimeError
   end

   def self.ord(name, value)
     self.class_eval "def #{name}() self[#{value-1}] end"
   end

   def method_missing(sym, *args, &block)
     index = ordinal_value(sym)
   rescue OrdinalNameError => ex
     super
   end

   ORDINALS = { "and" => 0 }

   %w(
     twenty thirty fourty fifty sixty seventy eighty ninety
   ).each_with_index do |name, index|
     ORDINALS[name] = 10 * (index+2)
   end

   %w(
     twentieth thirtieth fortieth fiftieth sixtieth
     seventieth eightieth ninetieth hundredth
   ).each_with_index do |name, index|
     ORDINALS[name] = 10 * (index+2)
   end

   %w(
     first second third fourth fifth sixth seventh
     eighth ninth tenth eleventh twelfth thirteenth
     fourteenth fifteenth sixteenth seventeenth
     eighteenth ninteenth twentieth
   ).each_with_index do |name, index|
     ORDINALS[name] = index + 1
   end

   %w(
     one two three four five six seven eight nine ten
     eleven twelve thirteen fourteen fifteen sixteen
     seventeen eighteen nineteen
   ).each_with_index do |name, index|
     ORDINALS[name] = index + 1
   end

   def ordinal_value(name)
     name = name.to_s.downcase
     if name !~ /_/
       ORDINALS[name]
     else
       terms = name.split(/_/)
       sum = 0
       while term = terms.shift
         if term =~ /^hundred(th)?$/
           sum *= 100
         elsif ORDINALS[term]
           sum += ORDINALS[term]
         else
           fail OrdinalNameError, "Unknown ordinal term '#{term}'"
         end
       end
       sum
     end
   end
end