Question

I am working with serialized array fields in one of my models, specifically in counting how many members of each array are shared.

Now, by the nature of my project, I am having to a HUGE number of these overlap countings.. so I was wondering if there was a super quick, cleaver way to do this.

At the moment, I am using the ‘&’ method, so my code looks like this

(user1.follower_names & user2.follower_names).count

which works fine… but I was hoping there might be a faster way to do it.

Answer 1

Sets are faster for this.

require 'benchmark'
require 'set'
alphabet = ('a'..'z').to_a
user1_followers = 100.times.map{ alphabet.sample(3) }
user2_followers = 100.times.map{ alphabet.sample(3) }
user1_followers_set = user1_followers.to_set
user2_followers_set = user2_followers.to_set

n = 1000
Benchmark.bm(7) do |x|
  x.report('arrays'){ n.times{ (user1_followers & user2_followers).size } }
  x.report('set'){ n.times{ (user1_followers_set & user2_followers_set).size } }
end

Output:

              user     system      total        real
arrays    0.910000   0.000000   0.910000 (  0.926098)
set       0.350000   0.000000   0.350000 (  0.359571)