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A Ruby reject! that returns the rejected items

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Jamie Hill

Posts: 161
Nickname: jamie007
Registered: Nov, 2006

Jamie Hill is Managing Director of SonicIQ Limited in the UK specialising in XHTML, CSS and Rails.

A Ruby reject! that returns the rejected items

Posted: Jul 25, 2007 4:25 AM

This post originated from an RSS feed registered with Ruby Buzz by Jamie Hill.
Original Post: A Ruby reject! that returns the rejected items Feed Title: The Lucid Feed URL: http://feeds.feedburner.com/thelucid Feed Description: Lightweight ramblings and tips on Ruby and Rails.	Latest Ruby Buzz Posts Latest Ruby Buzz Posts by Jamie Hill Latest Posts From The Lucid

I often need to do a reject! and return the rejected items instead of the modified collection. This saves having to do a select beforehand.

An example of how accomplish this:

options = { :a => 1, :b => 2, :c => 3 }
rejects = Hash[*options.select { |k, v| k == :b && options.delete(k) }.flatten]

assert_equal { :a => 1, :c => 3 }, options
assert_equal { :b => 2 }, rejects

This could be written as a method of the Hash class and an alternative for Array.

For Hash, the code would look something like:

class Hash
  def extract!
    Hash[*self.select { |k, v| yield(k, v) && self.delete(k) }.flatten]
  end
end

options = { :a => 1, :b => 2, :c => 3 }
rejects = options.extract! { |k, v| k == :b }

assert_equal { :a => 1, :c => 3 }, options
assert_equal { :b => 2 }, rejects

If I am missing something obvious in Ruby that accomplishes the same, please leave a comment.

Read: A Ruby reject! that returns the rejected items

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