From: Logan Capaldo <logancapaldo@...>
Date: 2006-07-21T12:28:23+09:00
Subject: Re: how to split an array in sub arrays of the same length


On Jul 20, 2006, at 4:40 PM, Phrogz wrote:

> Paolo Bacchilega wrote:
>> Is there a way to split an array in sub arrays of the same length,  
>> that
>
> Stolen from the facets[1] extensions for Arrays[2]:
>
> class Array
>   def each_slice(n=nil, &yld)
>     n = yld.arity.abs unless n
>     i=0
>     while i < self.length
>       yld.call(*self.slice(i,n))
>       i+=n
>     end
>   end
> end
>
> [1] http://facets.rubyforge.org/
> [2] http://facets.rubyforge.org/api/core/classes/Array.html#M000163
>
>

This is in enumerator, enumerator comes with ruby. Do we really need  
an "Optimized for Array" version?  (That is its purpose according to  
the docs.)

Well surprising to me, there really is a noticeable speed difference.
I gues sit makes sense, each_slice in enumerator.c is written to use  
each, and not just call to_a first either. (Which makes sense, Files  
are Enumerables after all, maybe you want it in chunks of N lines at  
a time. You wouldn't want to have to slurp the whole file into memory  
just to do that).

I wonder if we can get this each_slice stuck in the standard lib for  
Array.



% cat enumerator_vs_facets.rb
#!/usr/bin/env ruby
require 'enumerator'
require 'benchmark'

class Array
   def facets_each_slice(n=nil, &yld)
     n = yld.arity.abs unless n
     i=0
     while i < self.length
       yld.call(*self.slice(i,n))
       i+=n
     end
   end
end

arrays = [ (1..97).to_a, (0..99).to_a, ["hello", "world"] ]
N = 1000
Benchmark.bmbm do |bm|
   bm.report("Facets: ") do
     N.times do
       arrays.each do |array|
         array.facets_each_slice(3) { |*x| "#{x}" }
       end
     end
   end

   bm.report("Enumerator: ") do
     N.times do
       arrays.each do |array|
         array.each_slice(3) { |*x| "#{x}" }
       end
     end
   end
end



% ruby enumerator_vs_facets.rb
Rehearsal ------------------------------------------------
Facets:        1.250000   0.010000   1.260000 (  1.364671)
Enumerator:    1.380000   0.010000   1.390000 (  1.442132)
--------------------------------------- total: 2.650000sec

                    user     system      total        real
Facets:        1.250000   0.010000   1.260000 (  1.315879)
Enumerator:    1.390000   0.010000   1.400000 (  1.447592)