Shows the interesting intersections of followers between two Twitter users

twitter_intersect

#!/usr/bin/env ruby

# Usage:
# ./twitter_intersect username1 username2

# You'll need to `gem install twitter`
require 'twitter'

# see: https://dev.twitter.com/oauth/overview/application-owner-access-tokens
@client = Twitter::REST::Client.new do |config|
  config.consumer_key        = "CONSUMER_KEY"
  config.consumer_secret     = "CONSUMER_SECRET"
  config.access_token        = "ACCESS_TOKEN"
  config.access_token_secret = "ACCESS_SECRET"
end

def follower_ids(username)
  @client.follower_ids(username).to_a
end

def following_ids(username)
  @client.friend_ids(username).to_a
end

# this caches users to avoid looking up the same user
# multiple times
def users(user_ids)
  @users ||= {}
  result = []
  ids_to_lookup = []
  
  user_ids.each do |id|
    if @users[id] # already in cache
      result << @users[id]
    else # will need to be fetched
      ids_to_lookup << id
    end
  end
  
  # fetch all non-cached users at once
  new_users = @client.users(ids_to_lookup).to_a
  
  # update cache
  new_users.each do |user|
    @users[user.id] = user
  end
  
  (result + new_users)
end

def print_users(user_ids)
  users(user_ids)
    .map { |user| [user.screen_name, user.name ] }
    .map { |username, name| puts "#{username.ljust(20)}#{name}" }
end

def print_section(title, user_ids)
  puts "## #{title} (#{user_ids.size})"
  print_users(user_ids)
  puts "\n"
end

username1 = ARGV.shift
username2 = ARGV.shift

user1_follower_ids = follower_ids(username1)
user1_following_ids = following_ids(username1)

user2_follower_ids = follower_ids(username2)
user2_following_ids = following_ids(username2)

print_section(
  "Followers in common",
  user1_follower_ids & user2_follower_ids
)

print_section(
  "#{username1}'s followers that #{username2} follows", 
  user1_follower_ids & user2_following_ids
)

print_section(
  "#{username2}'s followers that #{username1} follows",
  user2_follower_ids & user1_following_ids
)

print_section(
  "Both following",
  user1_following_ids & user2_following_ids
)