Major changes in this commit over include work over several days but that was never...

[selectricity-live] / lib / randarray.rb

diff --git a/lib/randarray.rb b/lib/randarray.rb
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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