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Versions: 6
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Contents
class Array
unless method_defined?(:combination) # 1.8.7+
require 'facets/enumerator'
# Yields the block to each unique combination of _n_ elements.
#
# a = %w|a b c d|
# a.combination(3)
#
# produces
#
# [["a", "b", "c"],
# ["a", "b", "d"],
# ["a", "c", "d"],
# ["b", "c", "d"]]
#
# CREDIT: Florian Gross
def combination(k=2)
if block_given?
s = to_a
n = s.size
return unless (1..n) === k
idx = (0...k).to_a
loop do
yield s.values_at(*idx)
i = k - 1
i -= 1 while idx[i] == n - k + i
break if i < 0
idx[i] += 1
(i + 1 ... k).each {|j| idx[j] = idx[i] + j - i}
end
else
to_enum(:combination, k)
end
end
# OLD WAY
#a = []
#s = self
#n = s.size
#return unless (1..n) === k
#dx = (0...k).to_a
#loop do
# a << s.values_at(*idx)
# i = k - 1
# i -= 1 while idx[i] == n - k + i
# break if i < 0
# idx[i] += 1
# (i + 1 ... k).each {|j| idx[j] = idx[i] + j - i}
#end
#a
end
end
Version data entries
6 entries across 6 versions & 1 rubygems