# Merging two arrays

**URL:** <https://www.ruby-forum.com/t/merging-two-arrays/149206>\
**Category:** Ruby\
**Created:** [September 22, 2008, 3:10pm UTC](https://www.ruby-forum.com/t/merging-two-arrays/149206 "2008-09-22T15:10:44Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![crenner](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/278dde/32.png) [@crenner](https://www.ruby-forum.com/u/crenner)\
**Post date:** [September 22, 2008, 3:10pm UTC](https://www.ruby-forum.com/t/merging-two-arrays/149206/1 "2008-09-22T15:10:44Z")

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Hi,

in Ruby, I have two arrays:

products = Array.new  
products \<\< [“Amazon”,121212,“Harry Potter”]  
products \<\< [“Amazon”,242424,“John Grisham”]  
products \<\< [“Amazon”,353535,“Michael Crichton”]

links = Array.new  
links \<\< [121212,“[Amazon Book Clubs](http://www.amazon.com/abc)”]  
links \<\< [242424,“[www.amazon.com/johngrisham](http://www.amazon.com/johngrisham)”]  
links \<\< [353535,“[www.amazon.com/somelink](http://www.amazon.com/somelink)”]

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”,“[Amazon Book Clubs](http://www.amazon.com/abc)”]

Any help greatly appreciated.

Cheers, Chris

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<div class="post-metadata">

**Author:** ![crenner](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/278dde/32.png) [@crenner](https://www.ruby-forum.com/u/crenner)\
**Post date:** [September 22, 2008, 3:34pm UTC](https://www.ruby-forum.com/t/merging-two-arrays/149206/2 "2008-09-22T15:34:08Z")

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On Sep 22, 2008, at 9:02 AM, Chris C. wrote:

> links \<\< [121212,“[Amazon Book Clubs](http://www.amazon.com/abc)”]  
> Any help greatly appreciated.
> 
> Cheers, Chris

Treat links as an associative array, and use something like:

products.collect! {|p| p \<\< links.assoc(p[1])[1] }

I.e., look at the docs for Array#assoc

-Rob

Rob B. [http://agileconsultingllc.com](http://agileconsultingllc.com)  
removed\_email\_address@domain.invalid

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<div class="post-metadata">

**Author:** ![crenner](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/278dde/32.png) [@crenner](https://www.ruby-forum.com/u/crenner)\
**Post date:** [September 22, 2008, 3:34pm UTC](https://www.ruby-forum.com/t/merging-two-arrays/149206/3 "2008-09-22T15:34:45Z")

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On Mon, Sep 22, 2008 at 3:02 PM, Chris C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> links \<\< [121212,“[www.amazon.com/abc](http://www.amazon.com/abc)”]  
> links \<\< [242424,“[www.amazon.com/johngrisham](http://www.amazon.com/johngrisham)”]  
> links \<\< [353535,“[www.amazon.com/somelink](http://www.amazon.com/somelink)”]
> 
> 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”,“[Amazon Book Clubs](http://www.amazon.com/abc)”]

I assume you mean you want an array of three entries like the above one:

irb(main):017:0\> products.map {|x| x + links.assoc(x[1])[1…-1]}  
=\> [[“Amazon”, 121212, “Harry Potter”, “[Amazon Book Clubs](http://www.amazon.com/abc)”],  
[“Amazon”, 242424, “John Grisham”, “[www.amazon.com/johngrisham](http://www.amazon.com/johngrisham)”],  
[“Amazon”, 353535, “Michael Crichton”, “[www.amazon.com/somelink](http://www.amazon.com/somelink)”]]

The method assumes that in the products array, the id is in index 1,  
and in the links array it’s in index 0.  
Anyway, if you need to do many operations based on the id I suggest  
using a hash with the id as the key  
and an array (or Struct) as the value.

Hope this helps,

Jesus.

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<div class="post-metadata">

**Author:** ![crenner](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/278dde/32.png) [@crenner](https://www.ruby-forum.com/u/crenner)\
**Post date:** [September 22, 2008, 3:55pm UTC](https://www.ruby-forum.com/t/merging-two-arrays/149206/4 "2008-09-22T15:55:35Z")

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Chris C. 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”,“[Amazon Book Clubs](http://www.amazon.com/abc)”]

products.each do |product|  
id = product[1]  
links.each do |link|  
if link[0] == id  
product \<\< link[1]  
end  
end  
end

This will append the corresponding urls from the “links” array to the  
individual arrays held in the “products” array.

However, since you are already using an id, you might consider using a  
hash of hashes to store your data, for example:

products = {  
121212 =\> {  
:source =\> “Amazon”,  
:author =\> “John Grisham”,  
:url =\> nil  
}  
}

Later you can just change the :url value of an identified entry, using

products[121212][:url] = “[www.amazon.com/johngrisham](http://www.amazon.com/johngrisham)”

This will avoid having your data scattered about over numerous arrays  
and having to remember which field in which array holds the id value.  
Using hashes might be more straightforward in this case.

Henning

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<div class="post-metadata">

**Author:** ![crenner](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/278dde/32.png) [@crenner](https://www.ruby-forum.com/u/crenner)\
**Post date:** [September 22, 2008, 3:45pm UTC](https://www.ruby-forum.com/t/merging-two-arrays/149206/5 "2008-09-22T15:45:15Z")

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Chris C. 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”,“[Amazon Book Clubs](http://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,“[Amazon Book Clubs](http://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.