From: "Eric I." <rubytraining@...>
Date: 2008-05-29T04:48:31+09:00
Subject: Re: Merge collections of objects

On May 28, 8:55 am, John Butler <johnnybutl...@gmail.com> wrote:
> Hi,
>
> I wonder if there is a quick way to do this.
>
> companyA has 2 employees "a", "b"
>
> companyB has 3 employees "a", "b", "c"
>
> I basically want to merge companyA employess with companyB employees so
> when i look at companyA the employees will equal "a", "b", "c"

Hi John,

It's interesting that you used the word "collections" in your subject
rather than "arrays".  Because Ruby has options when it comes to
collections, and you can often gain something by choosing the best
collection for the job rather than always resorting to Arrays and
Hashes.

And it's also worth considering what types of operations you'll be
performing on these collections and how many members you expect to
deal with.  I don't know how Array#uniq is implemented, but it's most
typically implemented as an O(n**2) or it creates a supplementary data
structure (e.g., hash) to help it along.

The class Set is in the standard library, and as you might imagine a
set is a collection that does not allow duplicates and that does not
maintain order.  So it will automatically handle your "problem" of
duplicates.  The question is whether maintaining order is important to
your application or not.  And if you're merging a Set of size n into
one of size m, the merge is likely O(n) with no huge memory
requirement (as typically implemented).  So it's likely more efficient
at this operation.

Here's some sample code:

require 'set'

company_a = Set.new ['alice', 'bob', 'carla']
company_b = Set.new ['david', 'bob', 'ellen']

print "The employee(s) common to both companies is ",
      (company_a & company_b).to_a.join(', '), ".\n"

new_company = company_a + company_b
puts "If we create a new company with a union, we get " +
 
#{new_company.inspect}."

company_a.merge(company_b)
puts "If we merge one company into the other, we get "
+
  #{company_a.inspect}."

Eric

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