From: Dominik Bathon <dbatml@...>
Date: 2005-10-28T02:45:24+09:00
Subject: Re: [SUMMARY] Ducksay (#52)

On Thu, 27 Oct 2005 17:55:04 +0200, James Edward Gray II  
<james@grayproductions.net> wrote:

> On Oct 27, 2005, at 10:48 AM, Pit Capitain wrote:
>
>> Ruby Quiz schrieb:
>>
>>>     class String
>>>       def width
>>>         inject(0) {|w, line| [w, line.chomp.size].max }
>>>       end
>>>     end
>>> I just know I would have written width() as:
>>>     map { |line| line.chomp.size }.max
>>> Dave's is more efficient though.  It only ever keeps the highest  
>>> number, instead
>>> of building an Array of all the lengths.  Just one more reason  
>>> inject() is the
>>> one iterator to rule them all.  Thanks for trick #562, Dave!
>>>
>>
>> I'm not sure about the efficiency. The inject() version builds a new  
>> array on each pass, whereas the map() version builds only one array.  
>> Even an inject() implementation without the arrays was running slower  
>> than the map() implementation on my computer. inject() is nice, but it  
>> definitely doesn't rule them all (sorry Robert :-).
>
> I didn't make that very clear.
>
> I was speaking of memory consumption.  map() has to copy the whole  
> Array, while inject() does not.

I'm not sure what you mean with "copy the whole array". The Enumerable#map  
implementation just creates an empty array and adds all elements that the  
block returns to it.

One could argue that this leads to one big array (which still just  
contains Fixnums), while the arrays generated by the inject version can be  
garbage collected. But the inject version still allocates more memory  
overall.


And the map version is really faster:

require "benchmark"
include Benchmark

str = IO.read(ARGV.shift)

class String
	def width1
		inject(0) { |w, line| [w, line.chomp.size].max }
	end
	def width2
		map { |line| line.chomp.size }.max
	end
	def t1
		each { |line| [0, line.chomp.size] }
	end
	def t2
		each { |line| line.chomp.size }
	end
end

bmbm(4) { |x|
	x.report("w1") { str.width1 }
	x.report("w2") { str.width2 }
	x.report("t1") { str.t1 }
	x.report("t2") { str.t2 }
}

$ ruby str_width_bm.rb /usr/share/dict/words
Rehearsal ---------------------------------------
w1    1.200000   0.000000   1.200000 (  1.234289)
w2    0.790000   0.010000   0.800000 (  0.797576)
t1    0.960000   0.000000   0.960000 (  1.014776)
t2    0.730000   0.010000   0.740000 (  0.744466)
------------------------------ total: 3.700000sec

           user     system      total        real
w1    1.190000   0.010000   1.200000 (  1.231020)
w2    0.800000   0.000000   0.800000 (  0.809417)
t1    0.550000   0.000000   0.550000 (  0.556069)
t2    0.460000   0.010000   0.470000 (  0.500228)


Dominik