From: Mike Hall <mghallNO@...>
Date: 2004-08-03T04:26:34+09:00
Subject: Request for two methods in Array class


Two small requests:

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)

   For my use, I needed multiplication, but a block would be more general.

        a = [1,2,3]
        b = [1,3,5]
        a.combine(b)    => [1,6,15]

   Or with a block:

        a.combine(b) {|x,y| x*y}
  
   The new method would replace this sequence:

      a.zip(b).map {|e| e[0]*e[1]}
    or
      a.zip(b,c,d).map {|e| e.inject(1) {|prod, n| prod*n} }


2. A block initializer for Array.new, like that for Hash.new.
   Good for self-initializing a table of recurrence relations.
   
    a = Array.new() {|self, i|  2*self[i-1] - self[i-2]}

    a[0] = 1            # define the first two ...
    a[1] = x

    a[2]   =>  2x-1     # the rest are derived on the fly as needed
    a[3]   =>  ...


Hopefully, I'm not blind and haven't missed some obvious use
of the existing methods.  My apologies if that's the case.

Whatever...  just some thoughts.   Are they worth adding?

Thanks!