Module: ArrayStats

Included in:
Array
Defined in:
lib/array_stats.rb,
lib/array_stats/array_stats.rb

Constant Summary collapse

VERSION = 
'0.5.0'

Instance Method Summary collapse

Instance Method Details

#mean ⇒ Object

Returns the mean of all elements in array; nil if array is empty



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# File 'lib/array_stats/array_stats.rb', line 9

def mean
  if self.length == 0
    nil
  else
    self.total_sum / self.length
  end
end

#median ⇒ Object

Returns the median for the array; nil if array is empty



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# File 'lib/array_stats/array_stats.rb', line 18

def median
  percentile(50)
end

#percentile(p) ⇒ Object

Returns the percentile value for percentile p; nil if array is empty.

p should be expressed as an integer; percentile(90) returns the 90th percentile of the array.

Algorithm from NIST



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# File 'lib/array_stats/array_stats.rb', line 27

def percentile p
  sorted_array = self.sort
  rank = (p.to_f / 100) * (self.length + 1)
  
  if self.length == 0
    return nil
  elsif rank.fractional_part?
    sample_0 = sorted_array[rank.truncate - 1]
    sample_1 = sorted_array[rank.truncate]

    return (rank.fractional_part * (sample_1 - sample_0)) + sample_0
  else
    return sorted_array[rank - 1]
  end    
end

#total_sum ⇒ Object

Returns the sum of all elements in the array; 0 if array is empty



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# File 'lib/array_stats/array_stats.rb', line 4

def total_sum
  self.inject(0) {|sum, sample| sum += sample}
end