Module: DescriptiveStatistics::Spread

Included in:
AllMethods
Defined in:
lib/descriptive-statistics/spread.rb

Instance Method Summary collapse

Instance Method Details

#population_standard_deviation ⇒ Object 



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# File 'lib/descriptive-statistics/spread.rb', line 28

def population_standard_deviation
  return if length < 1
  Math.sqrt(population_variance)
end

#population_variance ⇒ Object 



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# File 'lib/descriptive-statistics/spread.rb', line 10

def population_variance
  return if length < 1
  precalculated_mean = mean
  sum = self.inject(0) {|accumulator, value| accumulator + (value - precalculated_mean) ** 2 }
  sum / length.to_f
end

#relative_standard_deviation ⇒ Object 



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# File 'lib/descriptive-statistics/spread.rb', line 22

def relative_standard_deviation
  return if length < 1
  precalculated_mean = mean
  (population_standard_deviation / precalculated_mean) * 100.0
end

#standard_deviation ⇒ Object 



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# File 'lib/descriptive-statistics/spread.rb', line 17

def standard_deviation
  return if length < 2
  Math.sqrt(variance)
end

#variance ⇒ Object 



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# File 'lib/descriptive-statistics/spread.rb', line 3

def variance
  return if length < 1
  precalculated_mean = mean
  sum = self.inject(0) {|accumulator, value| accumulator + (value - precalculated_mean) ** 2 }
  sum / (length.to_f - 1)
end

#zscore ⇒ Object 



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# File 'lib/descriptive-statistics/spread.rb', line 33

def zscore
  return if length < 2
  stdev = standard_deviation
  m = mean
  stdev.zero? ? Array.new(self.length, 0) : self.collect { |v| (v - m) / stdev }
end