Add bin and edit workflow

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

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+module Math
+
+  # Returns the percentile value for percentile _pcnt_; nil if array is empty.
+  #
+  # +pcnt+ should be expressed as an integer, e.g. `percentile(90)` returns
+  # the 90th percentile of the array.
+  #
+  # Algorithm from NIST[http://www.itl.nist.gov/div898/handbook/prc/section2/prc262.htm]
+  #
+  # NOTE: This is not a common core extension and is not
+  # loaded automatically when using <code>require 'facets'</code>.
+  #
+  # CREDIT: Ben Koski
+  #
+  # @non-core
+  #   require 'facets/array/precentile'
+  #
+  def self.percentile(array, pcnt)
+    sorted_array = array.sort
+
+    return nil if array.length == 0
+
+    rank  = (pcnt.to_f / 100) * (array.length + 1)
+    whole = rank.truncate
+ 
+    # if has fractional part
+    if whole != rank
+      s0 = sorted_array[whole - 1]
+      s1 = sorted_array[whole]
+
+      f = (rank - rank.truncate).abs
+
+      return (f * (s1 - s0)) + s0
+    else
+      return sorted_array[whole - 1]
+    end
+  end
+  
+end
+