Module: SimpleStats

Included in:
Array
Defined in:
lib/simple_stats.rb

Overview

Statistical methods to be used with numeric Arrays

Instance Method Summary collapse

Instance Method Details

#coefficient_of_variation ⇒ Object 



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# File 'lib/simple_stats.rb', line 25

def coefficient_of_variation
  mean = self.mean
  mean == 0 ? 0.0 : self.standard_deviation/mean
end

#histogram(num_of_bins = 20) ⇒ Object 



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# File 'lib/simple_stats.rb', line 48

def histogram(num_of_bins=20)
  min, max = self.min, self.max
  bin_width = Float(max-min)/num_of_bins
  bins = []
  num_of_bins.times do
    bins << (min..min+bin_width)
    min += bin_width
  end
  histohash = {}
  bins.each{ |b| histohash[b]=0 }
  self.each do |e|
    bin = bins.find{ |b| b.include? e }
    bin = bins.last unless bin # round off
    histohash[ bin ] += 1
  end
  histohash.sort do |x,y|
    0.5*(x[0].begin+x[0].end) <=> 0.5*(y[0].begin+y[0].end)
  end
end

#kurtosis ⇒ Object 



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# File 'lib/simple_stats.rb', line 37

def kurtosis
  mean, variance = self.mean, self.variance
  variance == 0 ? 0.0 :
    self.inject(0) { |sum, x| sum + (x-mean)**4 } /
    self.size / variance**2
end

#mean ⇒ Object 



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# File 'lib/simple_stats.rb', line 6

def mean
  self.inject(0) { |sum, x| sum + x.to_f / self.size }
end

#median ⇒ Object 



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# File 'lib/simple_stats.rb', line 10

def median
  sorted = self.sort
  mid = sorted.size / 2
  sorted.size % 2 == 0 ? [ sorted[mid], sorted[mid-1] ].mean : sorted[mid]
end

#percentile(percentage) ⇒ Object 



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# File 'lib/simple_stats.rb', line 44

def percentile(percentage)
  self.sort[ (self.size-1)*percentage/100 + 0.5 ]
end

#skewness ⇒ Object 



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# File 'lib/simple_stats.rb', line 30

def skewness
  mean, variance = self.mean, self.variance
  variance == 0 ? 0.0 :
    self.inject(0) { |sum, x| sum + (x-mean)**3 } /
    self.size / variance**(3/2.0)
end

#standard_deviation ⇒ Object 



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# File 'lib/simple_stats.rb', line 21

def standard_deviation
  Math::sqrt(self.variance)
end

#variance ⇒ Object 



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# File 'lib/simple_stats.rb', line 16

def variance
  mean = self.mean
  self.inject(0) { |sum, x| sum + (x-mean)**2 } / self.size 
end

#within?(tolerance, options = {}) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/simple_stats.rb', line 68

def within?(tolerance,options={})
  last_value = self.last
  max_difference = self.inject(0) do |max,value|
    difference = ( last_value - value ).abs
    max >= difference ? max : difference
  end
  scale = options[:percent] ? 100.0/last_value : 1
  scale = 0 if scale == 1.0/0
  max_difference * scale <= tolerance
end