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PQueue is a priority queue with array based heap. A priority queue is like a standard queue, except that each inserted element is given a certain priority, based on the result of the comparison block given at instantiation time. Also, retrieving an element from the queue will always return the one with the highest priority (see #pop and #top).

The default is to compare the elements in respect to their #<=> method. For example, Numeric elements with higher values will have higher priorities.

This library is a rewrite of the original PQueue.rb by K. Kodama and Heap.rb by Ronald Butler. The two libraries were later merged and generally improved by Olivier Renaud. Then the whole library rewritten by Trans using the original as a functional reference.


Usage is simple enough. Think of it as an array that takes a block, where the block decides which element of the array goes first.

require 'pqueue'

pq = PQueue.new([2,3,1]){ |a,b| a > b }

pq.pop  #=> 3


Using RubyGems:

gem install pqueue


Although the library has been completely rewritten since, we still would like to acknowledge the efforts of the original PQueue authors and contributors.

  • Olivier Renaud (2007)
  • Rick Bradley (2003)
  • Ronald Butler (2002)
  • K Kodama (2001, original library)

License & Copyrights

Copyright (c) 2011 Rubyworks

PQueue is distributable in accordance with the BSD-2-Clause license.

PQueue is based on the original PQueue library (c) 2001 by K. Kodama.

See the LICENSE.txt file for details.