Add bin and edit workflow

bin/gems/facets-3.1.0/lib/standard/facets/math/theil_index.rb

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+require 'facets/math/sum'
+require 'facets/math/mean'
+require 'facets/math/approx_equal'
+
+module Math
+
+  # Calculates the Theil index (a statistic used to measure
+  # economic inequality).
+  #
+  # TI = \sum_{i=1}^N \frac{x_i}{\sum_{j=1}^N x_j} ln \frac{x_i}{\bar{x}}
+  #
+  #   http://en.wikipedia.org/wiki/Theil_index
+  #
+  def self.theil_index(array)
+    return -1 if array.size <= 0 or any? { |x| x < 0 }
+    return  0 if array.size <  2 or all? { |x| approx_equal(x, 0) }
+    m = mean(array)
+    s = sum(array).to_f
+    inject(0) do |theil, xi|
+	    theil + ((xi > 0) ? (log(xi.to_f/m) * xi.to_f/s) : 0.0)
+    end
+  end
+
+end