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Contents
require 'more_math/ranking_common'
module MoreMath
class Subset
include Enumerable
include RankingCommon
# Returns a Subset instance for a collection of size +size+ with the rank
# +rank+.
def initialize(size, rank = 0)
@size, self.rank = size, rank
@last = (1 << size) - 1
end
# Returns the subset of the collection +collection+ for the rank +rank+.
def self.for(collection, rank = 0)
subset = new(collection.size, rank)
subset.instance_variable_set(:@collection, collection)
subset
end
# Returns the power set of the collection +collection+.
def self.power_set(collection)
self.for(collection).map(&:value)
end
# Assigns <code>m</code> to the rank attribute of this object.
def rank=(m)
@rank = m % (1 << size)
end
# Returns the subset for rank #rank and #collection. (If no collection was
# set it applies to the array [ 0, 1, ..., size - 1 ] instead.)
def value
result = []
c = @collection || (0...size).to_a
r = @rank
0.upto(size) do |i|
r[i] == 1 and result << c[i]
end
result
end
# TODO project
end
end
Version data entries
17 entries across 17 versions & 1 rubygems