From: Brian Candler <b.candler@...>
Date: 2008-09-22T22:37:05+09:00
Subject: Re: Merging two arrays

Chris Chris wrote:
> I would like to merge these two arrays. The article number is to be the
> identifier.
> 
> Thus, I would like an array like this as the result:
> ["Amazon",121212,"Harry Potter","www.amazon.com/abc"]

Are these two arrays already aligned and of the same size? If so just 
iterate using each_with_index, or look at Array#zip

If they are not aligned, or there are items in one list which are not in 
the other, then you need to be clearer about your requirements.

- What do you want to happen if an item is in 'products' but not in 
'links', or vice versa?

- What do you want to happen if there are multiple items in the 'links' 
list which match an item in the 'products' list, or vice versa?

One possibility:
* iterate across products.
* a product with no link gives a nil in the link column.
* a link with no product is ignored.
* if there are multiple links matching a product, only the first is 
used.

In that case you could just write:

products.each do |product|
  link = links.find { |link| link[0] == product[1] }
  product[3] = link ? link[1] : nil
end

If your links list is huge, it may be worth building a hash of 
article_number=>url first, rather than doing a linear search of the 
links array each time round.

But you may wish to consider a couple of other things first:

* make a class for Product and Link. Then you can say product.ref 
instead of product[1], link.url instead of link[1] etc. The code will be 
much easier to read.

* consider whether your article numbers are guaranteed unique across all 
suppliers. That is, is there any chance that Amazon have a book 121212 
and Waterstones have a different book that they also call 121212?

If so, maybe you want to change your links structure to

links << ["amazon",121212,"www.amazon.com/abc"]

In database-speak, ("amazon",121212) is a composite key.

If the article reference is an ISBN then that may be irrelevant. But 
ISBNs need to be strings I believe, due to use of the "X" character.
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