From: Ross Bamford <rossrt@...>
Date: 2006-03-30T00:32:17+09:00
Subject: Re: How to interator over two arrays?

On Thu, 2006-03-30 at 00:18 +0900, baumanj@gmail.com wrote:
> I don't see how this is an alternative for inject; it's just a
> different need. You use map when you want to generate a new Enumerable
> and inject when you want to generate a single value. The answer to the
> question "how does one iterate over multiple collections in parallel?"
> is just to use zip and the fact that assignment of an array to multiple
> variables puts the values of the elements into the variables.
> 

Glad you top posted this one, makes it easy to quote the original post:

> Ross Bamford wrote:
> > On Wed, 2006-03-29 at 13:28 +0900, brez! !! wrote:
> >
> > > I'm looking for a way to iterate over two arrays and sum or multiply or
> > > whatever each element resulting in a new array of the summed elements,
> > > e.g.
> > >
> > > a[0]+b[0], a[1]+b[1], ... a[n]+b[n]
> >

Notice OP wanted to sum or multiply each element *resulting in a new
array of summed elements*. Other solutions posted injected an array:

	arr.zip(brr).inject([]) { |ary,(a,b)| ary << a + b }

And I was just generally commenting that any time you inject an array
and want a one-for-one transformation you can avoid that and use map. I
obviously didn't mean that #map is a general-purpose alternative to
#inject...

> > Just a footnote to the other solutions you have for this, you can avoid
> > inject to make it a bit shorter using map (thanks to the way block
> > argument assignment works with arrays):
> >
> > ary = [1,2,3,4,5]
> > # => [1, 2, 3, 4, 5]
> >
> > bry = ary.dup
> > # => [1, 2, 3, 4, 5]
> >
> > ary.zip(bry).map! { |a,b| a+b }
> > # => [2, 4, 6, 8, 10]
> > 
> > -- 
> > Ross Bamford - rosco@roscopeco.REMOVE.co.uk

-- 
Ross Bamford - rosco@roscopeco.REMOVE.co.uk