This requires Ruby 1.9. It will run under 1.8 because uniq! will ignore the block, but it won't be correct.

multi_store_finder.rb

require 'yaml'

class Store
  attr_accessor :name, :address, :city, :state, :zip, :phone_number

  def unique_attributes
    [name[0..5], zip, phone_number, address[0..3]]
  end
end

def list_of_stores
  files = Dir.glob('*.yml')

  stores = []

  files.each do |file|
    File.open(file, 'r') {|f| stores += YAML.load(f)}
  end
  
  return stores
end

def delete_duplicates(stores)
  original_length = stores.length
  stores.uniq! {|s| s.unique_attributes}
  
  return original_length - stores.length
end

def print_multi_stores(stores)
  seen = {}

  stores.each do |store|
    if seen.has_key?(store.name)
      seen[store.name][0] += 1
    else
      seen[store.name] = [1, store.state]
    end
  end
  
  seen = seen.sort_by {|k,v| v[0]}
  
  seen.reverse!
  
  puts ""
  puts "multi stores"
  puts "-------------"
  
  #sorting converts hash to array of arrays
  seen.each do |k,v|
    num, state = v
    puts num.to_s + "--" + state + "--" + k  if num > 1
  end
  
  puts "-------------"
  puts ""
end

stores = list_of_stores

stores.sort_by! {|s| s.zip}

puts stores.length

puts "deleted " + delete_duplicates(stores).to_s + " duplicate stores"

print_multi_stores(stores)