0001-easy_set.rb

require 'set'

my_data = %w(cat cat dog dog foo bar bin baz baz bin)

my_set = Set.new

my_data.each do |i|
  if my_set.add?(i)
    puts "#{i} is the first of its kind"
  else
    puts "#{i} is already in the set"
  end
end

0002-cleaned_list.rb

require 'set'

class CleanedList
  def initialize
    @data = SortedSet.new
  end

  def to_a
    @data.to_a
  end

  def to_set
    @data
  end

  def <<(item)
    processed = item.to_s.downcase.strip.gsub(/\s{2,}/, '')
    @data << processed unless processed.nil? || processed == ""
  end

  alias_method :add, :<<

  def add?(item)
    processed = item.to_s.downcase.strip.gsub(/\s{2,}/, '')
    if processed.nil? || processed == ""
      return false
    else
      @data.add? processed
    end
  end
end

0003-cleaned_demo.rb

require './0002-cleaned_list.rb'

my_data = %w(Cat cat dog dOg foo BAR bin baz baz bin)

my_set = CleanedList.new

my_data.each do |i|
  if my_set.add?(i)
    puts "#{i} is the first of its kind"
  else
    puts "#{i} is already in the set"
  end
end

0004-fuzzy_match_class.rb

class FuzzyMatch
  class Matcher
    require 'singleton'
    require 'amatch'
    include Singleton

    def self.get_score(str1,str2)
      Amatch::JaroWinkler.new(str1).match(str2)
    end
  end

  class List
    require 'set'
    def initialize(options={})
      @options = {
        :filter     => //,
        :score      => 0.8,
        :downcase   => true,
        :ascii_only => true,
        :fix_spaces => true
      }.merge!(options)
      @data = Set.new
    end

    def to_a
      @data.to_a
    end

    def <<(item)
      item.downcase!              if @options[:downcase]
      item.gsub!(/[^a-z0-9 ]/,'') if @options[:ascii_only]
      item.gsub!(/\s{2,}/, '')    if @options[:fix_spaces]
      item.gsub!(@options[:filter], '')
      @data << item
    end

    alias_method :add, :<<

    def add?(item)
      item.downcase!              if @options[:downcase]
      item.gsub!(/[^a-z0-9 ]/,'') if @options[:ascii_only]
      item.gsub!(/\s{2,}/, '')    if @options[:fix_spaces]
      item.gsub!(@options[:filter], '')
      @data.add?(item)
    end

    def search(string)
      @data.to_a.select do |candidate|
        Matcher.get_score(string,candidate) > @options[:score]
      end
    end
  end
end

0005-fuzzy_match_demo.rb

require './0004-fuzzy_match_class.rb'

my_data = ["John Doe", "Jon Doe", "Jason Bourne", "Jason  Bourn ", " My Face", "My Space"]

my_list = FuzzyMatch::List.new

my_data.each do |i|
  if my_list.add?(i)
    puts "#{i} is the first of its kind"
    my_list.search(i).each do |m|
      puts "-> #{m} is also quite similar" unless m == i
    end
  else
    puts "#{i} is already in the set"
  end
end

Seems like processing in 2 should be its own method since you're doing the same thing in two different methods.

@janxios Yep, it should. Well, actually I probably should've taken the time to subclass Set...