gistfile1.rb

require 'digest/md5'

class RemoveDuplicateRecords < ActiveRecord::Migration
  def self.up
    addresses = {}
    Listing.find_each do |listing|
      digest = Digest::MD5.hexdigest("#{listing.street_address}#{listing.apartment_no}")
      if addresses.include?(digest) 
        listing.destroy
      else
        addresses[digest] = true
      end
    end
  end
end