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Select objects from arbitrary buckets matching any ol' percentage distribution.
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Simple distribution-based sampling of arbitrary objects from pools. Splashy. Pools. Get it!?

Disclaimer: I have a BFA in Art, so I'm convinced there's a far better algorithm than the awful one I came up with. Pull request button is thataway.

# Initialize with a desired final distribution.
buckets = :easy => 0.3, :hard => 0.7 )

# You can also specify a limit on elements in the final selection, no matter
# how many objects you collect.
buckets = {:easy => 0.3, :hard => 0.7}, 5 )

# Fill one-by-one:
buckets.add( :easy, obj1 )
buckets.add( :hard, obj2 )

# Fill using blocks:
i = 0
buckets.fill do |total_count|
  bucket = [:easy, :hard][total_count % 1]
  total_count < 100 ? [bucket, object] : nil
buckets.fill( :easy ) do |total_count|
  total_count < 105 ? object : nil

# Get a distribution of objects:
buckets = :a => 0.01, :b => 0.19, :c => 0.80 )
10.times { |i| buckets.add( :a, "1#{i}") }
2.times { |i| buckets.add( :b, "2#{i}") }
40.times { |i| buckets.add( :c, "3#{i}") }
# Returns:
#   {
#     :a => ["10"],
#     :b => ["20", "21"],
#     :c => ["30", "31", "32", "33", "34", "35", "36", "37"]
#   }

# Or even grab randomly: :random => true )


  • 0.1.2 - A few small bugs fixed in few-objects situations. (Thanks to Mars Hall)
  • 0.1.1 - Add support for random selection from buckets.
  • 0.1.0 - Several bug fixes, add #neediest_buckets method to Buckets to allow you to choose which buckets to add to first if an element can be put in multiple buckets, final distributions can now have empty buckets if it means we meet the wanted distribution better (i.e. a 99% to 1% wanted distribution with 5 and 1 elements, respectively, which will now select 4 and 0 elements if your wanted count is 4).
  • 0.0.2 - Raise ArgumentError when trying to add to a bucket that doesn't exist, don't consider an empty bucket "satisfied".
  • 0.0.1 - Initial release.


  • Check out the latest master to make sure the feature hasn't been implemented or the bug hasn't been fixed yet
  • Check out the issue tracker to make sure someone already hasn't requested it and/or contributed it
  • Fork the project
  • Start a feature/bugfix branch
  • Commit and push until you are happy with your contribution
  • Make sure to add tests for it. This is important so I don't break it in a future version unintentionally.
  • Please try not to mess with the Rakefile, version, or history. If you want to have your own version, or is otherwise necessary, that is fine, but please isolate to its own commit so I can cherry-pick around it.


Copyright (c) 2011 Tyson Tate. See LICENSE.txt for further details.

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