From: "Brian Schröder" <ruby.brian@...>
Date: 2005-08-08T17:16:06+09:00
Subject: Re: String#to_ary and Test::Unit

On 08/08/05, David A. Black <dblack@wobblini.net> wrote:
> Hi --
> 
> On Mon, 8 Aug 2005, Trans wrote:
> 
> > In Facets I offer:
> >
> >  class String
> >    def to_ary
> >      self.split(//)
> >    end
> >  end
> >
> > This proves useful in adding other methods to Enumerable that can act
> > to all enumerables and on strings as character arrays. For instance:
> >
> >  # Generates a hash mapping each unique element to the frequency it
> > appears.
> >  #--
> >  # Credit goes to Derek.
> >  #++
> >  def freq
> >    arr = respond_to?(:to_ary) ? self.to_ary : self.to_a
> >    probHash = Hash.new
> >    size = arr.size.to_f
> >    arr.uniq.each do |i|
> >      ct = arr.inject(0) do |mem,obj|
> >        obj.eql?(i) ? (mem+1) : mem
> >      end
> >      probHash[i] = ct.to_f/size
> >    end
> >    probHash
> >  end
> 
> This is just a sidenote, but here's a fun way to do that:
> 
>    module Enumerable
>      def freq
>        arr = to_ary rescue to_a
>        probs = Hash.new {|h,k| h[k] = arr.find_all {|e| e == k }.size }
>        arr.uniq.each {|k| probs[k] /= arr.size.to_f }
>        probs
>      end
>    end
> 
> :-)
> 

Another sidenote that removes the need for to_ary completely and is a
lot faster:

module Enumerable
  def freq_brian 
    probs = Hash.new(0.0)
    size = 0.0
    each do | e | 
      probs[e] += 1.0
      size += 1.0
    end
    probs.keys.each do | e | probs[e] /= size end
    probs
  end
end


      user     system      total        real
Derek  6.760000   0.790000   7.550000 (  8.286280)
David  4.100000   1.310000   5.410000 (  5.698582)
Brian  0.120000   0.010000   0.130000 (  0.134124)

require 'test/unit'

class TC_Frequency < Test::Unit::TestCase
  ARRAYS = [
  [1,2,1,1,1,4,5,6],
  [1,2,3,4],
  [],
  [0,0,0],
  Array.new(10) { rand(10) },
  Array.new(100) { rand(10) },
  Array.new(1000) { rand(10) }, 
  Array.new(10000) { rand(10) }, 
  Array.new(10000) { rand(100) }
  ] 

  def test_brian_david
    ARRAYS.each do | a |
      assert_equal(a.freq_david, a.freq_brian, "Brian's is not equal
to David's on #{a}")
    end
  end

  def test_brian_derek
    ARRAYS.each do | a |
      assert_equal(a.freq_derek, a.freq_brian, "Brian's is not equal
to Derek's on #{a}")
    end
  end
end

require 'benchmark'

Benchmark.bm do | b |
  b.report('Derek') do TC_Frequency::ARRAYS.each do | a | a.freq_derek end end
  b.report('David') do TC_Frequency::ARRAYS.each do | a | a.freq_david end end
  b.report('Brian') do TC_Frequency::ARRAYS.each do | a | a.freq_brian end end
end

regards,

Brian

-- 
http://ruby.brian-schroeder.de/

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