Module: MultiMeasure::MathHelpers

Defined in:
lib/multi_measure/math_helpers.rb

Overview

Copied from stackoverflow.com/questions/7749568/how-can-i-do-standard-deviation-in-ruby

Class Method Summary collapse

Class Method Details

.mean(a) ⇒ Object 



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# File 'lib/multi_measure/math_helpers.rb', line 8

def self.mean(a)
  sum(a) / a.length.to_f
end

.sample_variance(a) ⇒ Object 



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# File 'lib/multi_measure/math_helpers.rb', line 12

def self.sample_variance(a)
  m = mean(a)
  sum = a.inject(0){ |accum, i| accum + (i - m) ** 2 }
  sum / (a.length - 1).to_f
end

.standard_deviation(a) ⇒ Object 



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# File 'lib/multi_measure/math_helpers.rb', line 18

def self.standard_deviation(a)
  return 0.0 if a.length < 2
  Math.sqrt(sample_variance(a))
end

.sum(a) ⇒ Object 



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# File 'lib/multi_measure/math_helpers.rb', line 4

def self.sum(a)
  a.inject(0){ |accum, i| accum + i }
end