From: Robert Klemme <bob.news@...>
Date: 2004-08-03T17:56:33+09:00
Subject: Re: Request for two methods in Array class


"Yukihiro Matsumoto" <matz@ruby-lang.org> schrieb im Newsbeitrag
news:1091510011.625923.536.nullmailer@picachu.netlab.jp...
> Hi,
>
> In message "Request for two methods in Array class"
>     on 04/08/03, Mike Hall <mghallNO@SPAMenteract.com> writes:
>
> |1. A new method, Array.combine  (needs a better name for general use).
> |   It takes entries from two (or many) arrays and combines them.
> |   (like a combination of Array.zip, fetch, and map)
>
> Sounds nice.  But I'm not sure "combine" is a proper name for the
> method.   We need more discussion, for example:
>
>   * the best name for the behavior.

I like "combine" but I'm open to suggestions.

>   * whether it takes only one argument or any number of arguments.

IMHO n>=0

>   * whether "multiplication" should be the default.

No IMHO.

I imageine behavior similar to this:

class Array
  def combine(*arrays, &b)
    result = []
    each_with_index {|e,idx| result << b.call(e, *arrays.map {|ar|
ar[idx]})}
    result
  end
end

Note that arrays can contain anything that implements [], which might even
be a lambda (aka function):

a = [1,2,3]
a.combine(lambda {|i| i*2}) {|x,y| x*y}
=> [0, 4, 12]

So "arrays" might not be the ideal argument name.

Thinking a bit further about this it seems to me that the method might be
better put into Enumerable or Array as module method since arguments seem
to be symmetric:

class Array
  def self.combine(*arrays, &b)
    limit = arrays.inject(0){|l,a| s=a.size; s>l ? s : l}
    result = Array.new limit
    limit.times {|i| result[i] = b.call(*arrays.map {|ar| ar[i]}) }
    result
  end
end

irb(main):054:0> Array.combine([1,2,3],[1,3,5]) {|x,y| x*y}
=> [1, 6, 15]
irb(main):055:0> Array.combine([1,2,3],[1,3,5]) {|*x| x.inject(1){|z,i|
z*i} }
=> [1, 6, 15]

Kind regards

    robert