From: Phrogz <gavin@...>
Date: 2007-03-06T23:45:08+09:00
Subject: Re: remove duplicates of array of object based on a attribute

On Mar 6, 7:27 am, "Phrogz" <g...@refinery.com> wrote:
> Here's another (assumedly slower) version that doesn't rely on Set:

Huh...actually, the hash-based one seems faster than the Set-based
one:

  require 'set'
  class Array
    def uniq_by1
      seen = Set.new
      select{ |x| seen.add?( yield( x ) ) }
    end
    def uniq_by2
      seen = {}
      select{ |x| !seen[v=yield(x)] && (seen[v]=true) }
    end
  end

  require 'benchmark'
  a = [ {:a=>1, :d=>1}, {:b=>2}, {:c=>3}, {:a=>1, :d=>3},
        {:a=>2, :e=>7}, {:a=>3, :b=>2}, {:a=>1}, {:a=>4}, {:f=>6} ]
  N = 10_000
  Benchmark.bmbm{ |x|
    x.report( 'with_set' ){
      N.times{
        a.uniq_by1{ |h| h[:a] }
        a.uniq_by1{ |h| h[:b] }
      }
    }
    x.report( 'with_hash' ){
      N.times{
        a.uniq_by2{ |h| h[:a] }
        a.uniq_by2{ |h| h[:b] }
      }
    }
  }

  #=> Rehearsal ---------------------------------------------
  #=> with_set    1.840000   0.030000   1.870000 (  2.401238)
  #=> with_hash   1.270000   0.030000   1.300000 (  1.701307)
  #=> ------------------------------------ total: 3.170000sec
  #=>
  #=>                 user     system      total        real
  #=> with_set    1.820000   0.020000   1.840000 (  2.187477)
  #=> with_hash   1.250000   0.020000   1.270000 (  1.555490)

(Yes, my laptop is rather old and slow.)