Ruby example code for finding the intersection of two CSV files full of contacts (exported from Google contacts).

compare-contacts.rb

#!/usr/bin/ruby
# Usage: compare-contacts.rb [file1] [file2]
require 'csv'

def find_email_column_indexes(row) 
  [
    row.index('E-mail Address'),
    row.index('E-mail 2 Address'),
    row.index('E-mail 3 Address'),
    row.index('E-mail 1 - Value'),
    row.index('E-mail 2 - Value'),
    row.index('E-mail 3 - Value'),
    row.index('E-mail 4 - Value')
  ].compact
end

def read_contacts(file_name)
  i = 0
  emails = []
  email_indexes = nil
  CSV.foreach(file_name) do |row|
    if i == 0
      email_indexes = find_email_column_indexes(row)
      i += 1
      next
    end
    
    email_indexes.each do |j|
      email = row[j]
      # h[email] = (h[email] || 0) + 1 if email
      emails.push(email) if email and emails.index(email) == nil
    end
    i += 1
  end 
  emails
end

first_file_name = ARGV[0]
contacts1 = read_contacts first_file_name
puts first_file_name, contacts1.size

second_file_name = ARGV[1]
contacts2 = read_contacts second_file_name
puts second_file_name, contacts2.size

intersection = contacts1 & contacts2
puts intersection