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# Extends the Array class with a function used to randomly choose elements. Note that if you are using Rails, ActiveSupport recently was updated to include a similar
# function. This code checks for the presence of that method and does not try to replace it. They work the same though so no worries.
module RandomData
module ArrayRandomizer
# Randomly chooses an element from an array
# >> [1,2,3].rand = 3
# [].rand = nil
def rand
return self[Kernel.rand(self.size)]
end
# Takes an array of non-negative weights
# and returns the index selected by a
# roulette wheel weighted according to those
# weights.
# If a block is given then k is used to determine
# how many times the block is called. In this
# case nil is returned.
def roulette(k=1)
wheel = []
weight = 0
# Create the cumulative array.
self.each do |x|
raise "Illegal negative weight #{x}" if x < 0
wheel.push(weight += x)
end
# print "wheel is #{wheel.inspect}\n";
# print "weight is #{weight.inspect}\n";
raise "Array had all zero weights" if weight.zero?
wheel.push(weight + 1) #Add extra element
if block_given?
k.times do
r = Kernel.rand() # so we don't pick up that from array.
# print "r is #{r.inspect}\n";
roll = weight.to_f * r
# print "roll is #{roll.inspect}\n";
0.upto(self.size - 1) do |i|
if wheel[i+1] > roll
yield i
break
end # if
end # upto
end # if block_given?
return nil
else
r = Kernel.rand() # so we don't pick up that from array.
# print "r is #{r.inspect}\n";
roll = weight.to_f * r
# print "roll is #{roll.inspect}\n";
0.upto(self.size - 1) do |i|
return i if wheel[i+1] > roll
end
end
end
end
end
unless Array.respond_to?(:rand)
Array.send :include, RandomData::ArrayRandomizer
end
Version data entries
8 entries across 8 versions & 4 rubygems