From: Donovan Dillon <donovan.dillon@...>
Date: 2008-02-03T07:40:17+09:00
Subject: Re: Extracting vowels and consonants using regular expression

Thanks Robert, Corey, Philip, Stephano, et. al, for all of the great
suggestions. However, they all seem to ignore the conditional nature of 'y'
as a vowel. I would like the regex to treat 'y' as a vowel when there is no
other vowel either before or after it. The string I used initially, was
drawn from the following perl code that accomplishes this (found at
http://www.perlmonks.org/?node_id=592867):


my @vowels = ( /[aeiou]|(?<![aeiou])y(?![aeiou])/gi );

The "(?<!...)" is a "zero-width negative-look-behind assertion".

The "(?!...)" is a "zero-width negative-look-ahead assertion".

Together, they match the condition of treating "y as a vowel only if there
is no other vowel before or after it."


This was my attempt at converting the Perl fragment to Ruby syntax:

scan(/[aeiou]|(?![aeiou])y(?![aeiou])/i)

I have since discovered that Ruby 1.8 lacks regex look-behind assertion --
which explains why the code was failing. As a result, I have fallen back to
the following which currently ignores the 'y':

class String
  def vowels
    scan(/[aeiou]/i)
  end
  def consonants
    scan(/[^aeiou]/i)
  end
end


Any ideas how to modify this to include the conditional treatment of "y as a
vowel only if there is no other vowel before or after it?"

(i.e., is there a way to simulate the perl "zero-width negative-look-behind"
and "zero-width negative-look-ahead" assertions for 'y' in Ruby 1.8?)


On 2/2/08 4:17 PM, in article
335e48a90802021417n4ba96a11i746bd5118f18464e@mail.gmail.com, "Robert Dober"
<robert.dober@gmail.com> wrote:

> Oh sorry using 1.9 excluseviley now...
> Robert
>