Method: Ai4r::Data::Statistics.variance

Defined in:
lib/ai4r/data/statistics.rb

.variance(data_set, attribute, mean = nil) ⇒ Object

Get the variance. You can provide the mean if you have it already, to speed up things.



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# File 'lib/ai4r/data/statistics.rb', line 29

def self.variance(data_set, attribute, mean = nil)
  index = data_set.get_index(attribute)
  mean = mean(data_set, attribute)
  sum = 0.0
  data_set.data_items.each { |item| sum += (item[index]-mean)**2 }
  return sum / (data_set.data_items.length-1)
end