From: daz <dooby@...10.karoo.co.uk>
Date: 2005-10-13T21:56:56+09:00
Subject: Re: array1 + array2 newb question


Robert Klemme wrote:
> Kroeger, Simon (ext) wrote:
> >> From: Robert Klemme [mailto:bob.news@gmx.net]
> >> Since there hasn't been an #inject solution so far... :-)
> >
> > hmm, is the gateway broken again?
> >
> > a1.inject([]){|s, x| s + a2.map {|y| [x, y]}}
> >
> > (posted 1 hour ago)
>
> No, it's here.  Can't tell though whether I just overlooked it
> or whether the posting arrived here after I wrote mine.
>
> And note that your version has the disadvantage [...]


A more significant disadvantage is that you both posted solutions
with equivalent results but for a slightly different problem than
the one posed by the OP ;)

> [...] that you copy s all the time.

As did my solution.

> Using concat is more efficient.

That's usually safe to say ... but check the b/marks.

>  That's why my solution just appends two element arrays to
> the collecting array. :-)

.... And ends up 3rd out of 3 in the b/mk race  :-D

>
> Kind regards
>
>     robert
>

After making the necessary corrections:

#--------------------
require 'benchmark'
include Benchmark

a1 = [1,2,3]
a2 = %w{a b c}

BMN = 50000  # <------ ?whatever?
bm(7) do |bx|
  bx.report('d-') { BMN.times { dz = []; a2.each{|s| dz += a1.map {|y| [y, s]}}       }}
  bx.report('s-') { BMN.times { sk = a2.inject([]){|s,x| s + a1.map {|y| [y, x]}}     }}
  bx.report('r-') { BMN.times { rk = a2.inject([]){|r,x| a1.each {|y| r << [y,x]}; r} }}
    GC.start ; GC.disable
  bx.report('dz') { BMN.times { dz = []; a2.each{|s| dz += a1.map {|y| [y, s]}}       }}
    GC.start ; GC.disable
  bx.report('sk') { BMN.times { sk = a2.inject([]){|s,x| s + a1.map {|y| [y, x]}}     }}
    GC.start ; GC.disable
  bx.report('rk') { BMN.times { rk = a2.inject([]){|r,x| a1.each {|y| r << [y,x]}; r} }}
end

=begin
             user     system      total        real
d-       5.857000   0.000000   5.857000 (  5.880000)
s-       7.145000   0.000000   7.145000 (  7.140000)
r-       8.040000   0.000000   8.040000 (  8.070000)
dz       5.415000   0.000000   5.415000 (  5.440000)
sk       6.428000   0.000000   6.428000 (  6.420000)
rk       7.353000   0.000000   7.353000 (  7.360000)
=end
#--------------------

IMHO - #inject is very useful but I don't see the advantage
       of using it to hide an initial  x = []  and
       subjecting it to being flung round in circles.

As you can see, it doesn't gain anything, here.

(Not a squabble :-)

daz