From: Armin Armbruster <aarmbruster@...>
Date: 2008-11-08T05:52:47+09:00
Subject: Re: How to operate on 2 arrays simultaneously?

I just ran into a similar problem, and I thought it fits into this 
thread.

The Vector class defines the collect2() and collect2!() methods, which 
conceptually I like very much. So I thought I could just use the same 
concept and extend Array like this:

class Array
  def collect2(v) # :yield: e1, e2
    Array.Raise ErrDimensionMismatch if size != v.size
    (0 .. size - 1).collect do
      |i|
      yield self[i], v[i]
    end
  end

  def collect2!(v) # :yield: e1, e2
   Array.Raise ErrDimensionMismatch if size != v.size
    (0 .. size - 1).collect do
      |i|
      self[i] = yield self[i], v[i]
    end
  end
end

After this I can simply do:
a = [1,2,3]
b = [4,5,6]
a.collect2(b){|e1,e2| e1+e2}
=> [5, 7, 9]

Does anybody see anything wrong with this?
If not, it seems such a handy concept that I'm surprised these are not 
standard methods of Array. I've had this problem in various forms over 
the past and typically reverted to Array#each_index, always thinking 
that this is too clumsy for Ruby, but until now I never took the time to 
come up with something more elegant (not that I want to take any credit 
for this suggestion as I simply copied what's already in Vector).




Todd Benson wrote:
> On Thu, Sep 11, 2008 at 2:02 PM, Peter Bunyan <peter.bunyan@gmail.com> 
> wrote:
>>
>> http://www.ruby-doc.org/stdlib/libdoc/matrix/rdoc/classes/Matrix.html
> 
> Yeah, that's probably what I would do for a simple script.  I haven't
> checked memory usage, but it is elegant IMHO.  Probably best for very
> large arrays.
> 
> a = 1, 2, 3, 4
> b = 4, 3, 2, 1
> (Matrix[a] + Matrix[b]).to_a.flatten
> 
> => [5, 5, 5, 5]
> 
> Todd

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