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Descriptive Statistics

Overview

This gem adds methods to the Enumerable module to allow easy calculation of basic descriptive statistics of Numeric sample data in collections that have included Enumerable such as Array, Hash, Set, and Range. The statistics that can be calculated are:

  • Number
  • Sum
  • Mean
  • Median
  • Mode
  • Variance
  • Standard Deviation
  • Percentile
  • Percentile Rank
  • Descriptive Statistics
  • Quartiles

When requiring DescriptiveStatistics, the Enumerable module is monkey patched so that the statistical methods are available on any instance of a class that has included Enumerable. For example with an Array:

> require 'descriptive_statistics'
 => true 
> data = [2,6,9,3,5,1,8,3,6,9,2]
 => [2, 6, 9, 3, 5, 1, 8, 3, 6, 9, 2] 
> data.number
 => 11.0 
> data.sum
 => 54.0
> data.mean
 => 4.909090909090909 
> data.median
 => 5.0 
> data.variance
 => 7.7190082644628095 
> data.standard_deviation
 => 2.778310325442932 
> data.percentile(30)
 => 3.0 
> data.percentile(70)
 => 6.0
> data.percentile_rank(8)
 => 81.81818181818183
> data.mode
 => 2
> data.range
 => 8
> data.descriptive_statistics
 => {:number=>11.0, 
  :sum=>54, 
  :variance=>7.7190082644628095, 
  :standard_deviation=>2.778310325442932, 
  :min=>1, 
  :max=>9, 
  :mean=>4.909090909090909, 
  :mode=>2, 
  :median=>5.0, 
  :range=>8.0, 
  :q1=>2.5, 
  :q2=>5.0, 
  :q3=>7.0}

and with other types of objects:

> require 'set'
=> true 
> require 'descriptive_statistics'
=> true 
> {:a=>1, :b=>2, :c=>3, :d=>4, :e=>5}.mean #Hash
=> 3.0 
> Set.new([1,2,3,4,5]).mean #Set
=> 3.0 
> (1..5).mean #Range
=> 3.0

including instances of your own classes, when an each method is provided that creates an Enumerator over the sample data to be operated upon:

class Foo 
  include Enumerable
  attr_accessor :bar, :baz, :bat

  def each
    [@bar, @baz, @bat].each
  end
end

foo = Foo.new
foo.bar = 1
foo.baz = 2
foo.bat = 3
foo.mean
=> 2.0

or:

class Foo 
  include Enumerable
  attr_accessor :bar, :baz, :bat

  def each
    Enumerator.new do |y|
      y << @bar
      y << @baz
      y << @bat
    end
  end
end

foo = Foo.new
foo.bar = 1
foo.baz = 2
foo.bat = 3
foo.mean
=> 2.0

and even Structs:

Scores = Struct.new(:sally, :john, :peter)
bowling = Scores.new
bowling.sally = 203
bowling.john = 134
bowling.peter = 233
bowling.mean
=> 190.0

Alternatively, you can extend DescriptiveStatistics on individual objects by requiring DescriptiveStatistics safely, thus avoiding the monkey patch. For example:

> require 'descriptive_statistics/safe'
 => true
> data = [2,6,9,3,5,1,8,3,6,9,2]
 => [2, 6, 9, 3, 5, 1, 8, 3, 6, 9, 2] 
> data.extend(DescriptiveStatistics)
 => [2, 6, 9, 3, 5, 1, 8, 3, 6, 9, 2] 
> data.number
 => 11.0 
> data.sum
 => 54

Or if you prefer leaving your collection pristine

> require 'descriptive_statistics/safe'
 => true 
> stats = DescriptiveStatistics::Stats.new([1,2,3,4,5,1])
 => #<DescriptiveStatistics::Stats:0x00000101a38228 @collection=[1, 2, 3, 4, 5, 1]> 
> stats.mean
 => 2.6666666666666665 
> stats.median
 => 2.5 
> stats.mode
 => 1

Notes

  • All methods return a Float object except for mode, which will return a Numeric object from the collection.
  • All methods return nil when the collection is empty, except for number, which returns 0.0 (This is a different behavior than ActiveSupport's Enumerable monkey patch of sum, which by deafult returns the Fixnum 0 for empty collections. This may be an issue for you if you are using Rails.)

Ports

Javascript

Python

Go

Elixir

Clojure

License

Copyright (c) 2010-2014 Derrick Parkhurst (derrick.parkhurst@gmail.com), Gregory Brown (gregory.t.brown@gmail.com), Daniel Farrell (danielfarrell76@gmail.com), Graham Malmgren, Guy Shechter

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.