From: Julian Leviston <julian@...>
Date: 2008-03-31T12:49:20+09:00
Subject: Re: inject's pathological case...

...or you could do it like this:

def collect_repeats_inject(list)
   return list unless list.respond_to?(:inject)
   collected_hash = list.inject({}) do |collected_repeats, item|
     ( collected_hash[item] ||= [] ) << item
     collected_hash
   end
   collected_hash.values
end

On 30/03/2008, at 8:55 PM, William James wrote:

> On Mar 30, 12:27 am, 7stud -- <bbxx789_0...@yahoo.com> wrote:
>> Oh, yeah:
>>
>> $ ruby -v
>> ruby 1.8.2 (2004-12-25) [universal-darwin8.0]
>>
>> By the way, using inject() is inefficient--not to mention confusing.
>> You might as well pretend it doesn't exist.
>
> There is some truth to that.
>
>
> def collect_repeats_inject list
>  return [] if [] == list
>  list[1..-1].inject([[ list.first ]]){|a,e|
>    if a[-1][0] == e
>      a[-1] << e
>    else
>      a << [e]
>    end
>    a
>  }.reject{|lst|  lst.size < 2 }
> end
>
> def collect_repeats list
>  accum = [ [ list.shift ] ]
>  list.each{|e|
>    if accum[-1][0] == e
>      accum[-1] << e
>    else
>      accum << [e]
>    end }
>  accum.reject{|lst|  lst.size < 2 }
> end
>
> p collect_repeats( %w(0 1 1 2 3 3 3 3 4 5 5 6) )
> p collect_repeats( [] )
> p collect_repeats_inject( %w(0 1 1 2 3 3 3 3 4 5 5 6) )
> p collect_repeats_inject( [] )
>
> the_list =  %w(0 1 1 2 3 3 3 3 3 3 3 3 4 5 5 6 7 8 8 9 9 9)
>
> t = Time.now
> 9999.times{ collect_repeats_inject( the_list )}
> p Time.now - t
> t = Time.now
> 9999.times{ collect_repeats( the_list )}
> p Time.now - t
>
> --- output ---
> [["1", "1"], ["3", "3", "3", "3"], ["5", "5"]]
> []
> [["1", "1"], ["3", "3", "3", "3"], ["5", "5"]]
> []
> 2.694
> 0.16
>
>
> And the version without inject is shorter and
> clearer.
>