An atlrug member asked for a code-review so I made a couple of changes and suggestions

multi_store_finder.rb

require 'yaml'

class Store
  attr_accessor :name, :address, :city, :state, :zip, :phone_number
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)
  seen = []
  
  marker = []

  counter = 0
  
  stores.each do |store|
    attr_array = [store.name[0..5], store.zip, store.phone_number, store.address[0..3]]

    if seen.include?(attr_array)
      marker << store
      counter += 1
    else
      seen << attr_array
    end 
  end
  
  marker.each {|m| stores.delete(m)}
  
  return counter
end

def print_multi_stores(stores)
  seen = Hash.new { |h,k| h[k] = Hash.new(0) }

  stores.each do |store|
    seen[store.name][store.state] += 1
  end
  
  seen = seen.sort_by {|k,v| v[0]}
  
  seen.reverse!
  
  puts ""
  puts "multi stores"
  puts "-------------"
  
  seen.each do |store_name,state_counts|
    total_stores = state_counts.values.reduce(0) { |sum, val| sum += val }
    next if total_stores < 2

    puts "#{store_name}: #{total_stores} stores"
    state_counts.each do |state,count|
      puts "\t#{state} -- #{count}"
    end

  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)