class Array
  #sum (and mean) found on http://snippets.dzone.com/posts/show/2161
  def sum
    inject( nil ) { |sum,x| sum ? sum + x.to_f : x.to_f }
  end
  
  def mean
    sum.to_f / size
  end
  
  #http://en.wikipedia.org/wiki/Mean#Weighted_arithmetic_mean
  def weighted_mean(weights_array)
    raise "Each element of the array must have an accompanying weight.  Array length = #{self.size} versus Weights length = #{weights_array.size}" if weights_array.size != self.size
    w_sum = weights_array.sum
    w_prod = 0
    self.each_index {|i| w_prod += self[i] * weights_array[i].to_f}
    w_prod.to_f / w_sum.to_f
  end
end

>> a = [1,2,3]
=> [1, 2, 3]
>> w = [1,1,1]
=> [1, 1, 1]
>> a.weighted_arithmetic_mean(w)
=> 2.0
>> a.mean
=> 2.0
>> w = [5,2,1]
=> [5, 2, 1]
>> a.weighted_arithmetic_mean(w)
=> 1.5

class String
  def chunk_string(average_segment_size = 40, sclice_on = /\s+/)
    out = []
    slices_estimate = self.size.divmod(average_segment_size)
    slice_count = (slices_estimate[1] > 0 ? slices_estimate[0] + 1 : slices_estimate[0])
    slice_guess = self.size / slice_count
    previous_slice_location = 0
    (1..slice_count - 1).each do
      |i|
      slice_location = self.nearest_split(slice_guess * i, sclice_on)
      out << self.slice(previous_slice_location..slice_location)
      previous_slice_location = slice_location + 1
    end
    out << self.slice(previous_slice_location..self.size)
    out
  end

  def nearest_split(slice_start, slice_on)
    left_scan_location  = (self.slice(0..slice_start).rindex(slice_on)).to_i
    right_scan_location = (self.slice((slice_start+1)..self.size).index(slice_on)).to_i + slice_start
    ((slice_start - left_scan_location) < (right_scan_location - slice_start) ? left_scan_location : right_scan_location)
  end
end