# Weighted Random Methods For Array

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class Array
# Chooses a random array element from the receiver based on the weights
# provided. If _weights_ is nil, then each element is weighed equally.
#
# [1,2,3].random #=> 2
# [1,2,3].random #=> 1
# [1,2,3].random #=> 3
#
# If _weights_ is an array, then each element of the receiver gets its
# weight from the corresponding element of _weights_. Notice that it
# favors the element with the highest weight.
#
# [1,2,3].random([1,4,1]) #=> 2
# [1,2,3].random([1,4,1]) #=> 1
# [1,2,3].random([1,4,1]) #=> 2
# [1,2,3].random([1,4,1]) #=> 2
# [1,2,3].random([1,4,1]) #=> 3
#
# If _weights_ is a symbol, the weight array is constructed by calling
# the appropriate method on each array element in turn. Notice that
# it favors the longer word when using :length.
#
# ['dog', 'cat', 'hippopotamus'].random(:length) #=> "hippopotamus"
# ['dog', 'cat', 'hippopotamus'].random(:length) #=> "dog"
# ['dog', 'cat', 'hippopotamus'].random(:length) #=> "hippopotamus"
# ['dog', 'cat', 'hippopotamus'].random(:length) #=> "hippopotamus"
# ['dog', 'cat', 'hippopotamus'].random(:length) #=> "cat"
def random(weights=nil)
return random(map {|n| n.send(weights)}) if weights.is_a? Symbol
weights ||= Array.new(length, 1.0)
total = weights.inject(0.0) {|t,w| t+w}
point = rand * total
zip(weights).each do |n,w|
return n if w >= point
point -= w
end
end
# Generates a permutation of the receiver based on _weights_ as in
# Array#random. Notice that it favors the element with the highest
# weight.
#
# [1,2,3].randomize #=> [2,1,3]
# [1,2,3].randomize #=> [1,3,2]
# [1,2,3].randomize([1,4,1]) #=> [2,1,3]
# [1,2,3].randomize([1,4,1]) #=> [2,3,1]
# [1,2,3].randomize([1,4,1]) #=> [1,2,3]
# [1,2,3].randomize([1,4,1]) #=> [2,3,1]
# [1,2,3].randomize([1,4,1]) #=> [3,2,1]
# [1,2,3].randomize([1,4,1]) #=> [2,1,3]
def randomize(weights=nil)
return randomize(map {|n| n.send(weights)}) if weights.is_a? Symbol
weights = weights.nil? ? Array.new(length, 1.0) : weights.dup
# pick out elements until there are none left
list, result = self.dup, []
until list.empty?
# pick an element
result << list.random(weights)
# remove the element from the temporary list and its weight
weights.delete_at(list.index(result.last))
list.delete result.last
end
result
end
end
```

Intended for use in selecting random elements from an array based on weight. Not optimized!

Data structure

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