From: Phrogz <gavin@...>
Date: 2007-03-06T23:30:07+09:00
Subject: Re: remove duplicates of array of object based on a attribute

On Mar 6, 7:03 am, senthil <senthilku...@srishtisoft.com> wrote:
> hi all,
>           how to remove duplicates of an array of objects based a
> attribute of the object. For ex
>            i am having an array of  ruby beans named diagnoses . i want
> remove duplicates from the based on the diagnoses id. assume diagnoses
> have attributes id and weightage .So for two diagnoses with same id and
> different weightage , the diagnoses with lower weightage should be
> removed.

Here's my best shot at it:

require 'set'
class Array
  def uniq_by
    seen = Set.new
    select{ |x| seen.add?( yield( x ) ) }
  end
end

a = [ {:a=>1, :d=>1}, {:b=>2}, {:c=>3}, {:a=>1, :d=>3} ]
p a, a.uniq, a.uniq_by{ |h| h[:a] }
#=> [{:a=>1, :d=>1}, {:b=>2}, {:c=>3}, {:a=>1, :d=>3}]
#=> [{:a=>1, :d=>1}, {:b=>2}, {:c=>3}, {:a=>1, :d=>3}]
#=> [{:a=>1, :d=>1}, {:b=>2}]

(Note how :b=>2 and :c=>3 have the same value for :a (nil), so only
one is included.)

Here's another (assumedly slower) version that doesn't rely on Set:

class Array
  def uniq_by
    seen = {}
    select{ |x|
      v = yield(x)
      !seen[v] && (seen[v]=true)
    }
  end
end