Feature/string attributes

.rspec

@@ -1,2 +1,3 @@
 --format documentation
 --color
+--order rand

lib/weka/classifiers/evaluation.rb

@@ -11,6 +11,7 @@ class Evaluation
 
       alias summary                 to_summary_string
       alias class_details           to_class_details_string
+      alias confusion_matrix        to_matrix_string
 
       alias instance_count          num_instances
       alias correct_count           correct

lib/weka/core/attribute.rb

@@ -1,23 +1,82 @@
+require 'weka/concerns/persistent'
+
 module Weka
   module Core
     java_import 'weka.core.Attribute'
 
     class Attribute
+      include Weka::Concerns::Persistent
+
+      TYPES = %i(numeric nominal string date).freeze
+
+      class << self
+        def new_numeric(name)
+          new(name.to_s)
+        end
+
+        def new_nominal(name, values)
+          new(name.to_s, Array(values).map(&:to_s))
+        end
+
+        def new_date(name, format)
+          new(name.to_s, format.to_s)
+        end
+
+        ##
+        # Creates a new Attribute instance of type string.
+        #
+        # The java class defines the same constructor:
+        # Attribute(java.lang.String, java.util.List<java.lang.String>)
+        # for nominal and string attributes and handles the type internally
+        # based on the second argument.
+        #
+        # In Java you would write following code to create a string Attribute:
+        #   Attribute attribute = new Attribute("name", (FastVector) null);
+        #
+        # When we use a similar approach in JRuby:
+        #   attribute = Attribute.new('name', nil)
+        # then a Java::JavaLang::NullPointerException is thrown.
+        #
+        # Thus, we use refelection here and call the contructor explicitly, see
+        # https://github.com/jruby/jruby/wiki/CallingJavaFromJRuby#constructors
+        #
+        # The object returned from Java constructor only has class
+        # Java::JavaObject so we need to cast it to the proper class
+        #
+        # See also:
+        # https://stackoverflow.com/questions/1792495/casting-objects-in-jruby
+        def new_string(name)
+          constructor = Attribute.java_class.declared_constructor(
+            java.lang.String,
+            java.util.List
+          )
+
+          constructor.new_instance(name.to_s, nil).to_java(Attribute)
+        end
+      end
+
       def values
         enumerate_values.to_a
       end
 
+      ##
+      # Returns the string representation of the attribute's type.
+      # Overwrites the weka.core.Attribute type Java method, which returns an
+      # integer representation of the type based on the defined type constants.
+      def type
+        self.class.type_to_string(self)
+      end
+
+      ##
       # The order of the if statements is important here, because a date is also
       # a numeric.
       def internal_value_of(value)
         return value                      if value === Float::NAN
         return Float::NAN                 if [nil, '?'].include?(value)
         return parse_date(value.to_s)     if date?
         return value.to_f                 if numeric?
-        return index_of_value(value.to_s) if nominal?
+        return index_of_value(value.to_s) if nominal? || string?
       end
     end
-
-    Weka::Core::Attribute.__persistent__ = true
   end
 end

lib/weka/core/dense_instance.rb

@@ -61,7 +61,7 @@ def value_from(value, index)
           format_date(value, attribute.date_format)
         elsif attribute.numeric?
           value
-        elsif attribute.nominal?
+        elsif attribute.nominal? || attribute.string?
           attribute.value(value)
         end
       end

lib/weka/core/instances.rb

@@ -62,9 +62,29 @@ def add_attributes(&block)
         self
       end
 
-      alias with_attributes  add_attributes
-      alias instances_count  num_instances
-      alias attributes_count num_attributes
+      alias with_attributes       add_attributes
+      alias instances_count       num_instances
+      alias attributes_count      num_attributes
+      alias has_string_attribute? check_for_string_attributes
+
+      ## Check if the instances has any attribute of the given type
+      # @param [String, Symbol, Integer] type type of the attribute to check
+      #   String and Symbol argument are converted to corresponding type
+      #   defined in Weka::Core::Attribute
+      #
+      # @example Passing String
+      #   instances.has_attribute_type?('string')
+      #   instances.has_attribute_type?('String')
+      #
+      # @example Passing Symbol
+      #   instances.has_attribute_type?(:String)
+      #
+      # @example Passing Integer
+      #   instances.has_attribute_type?(Attribute::STRING)
+      def has_attribute_type?(type)
+        type = map_attribute_type(type) unless type.is_a?(Integer)
+        check_for_attribute_type(type)
+      end
 
       def each
         if block_given?
@@ -120,25 +140,25 @@ def to_c45(file)
       end
 
       def numeric(name, class_attribute: false)
-        attribute = Attribute.new(name.to_s)
+        attribute = Attribute.new_numeric(name)
         add_attribute(attribute)
         self.class_attribute = name if class_attribute
       end
 
       def nominal(name, values:, class_attribute: false)
-        attribute = Attribute.new(name.to_s, Array(values).map(&:to_s))
+        attribute = Attribute.new_nominal(name, values)
         add_attribute(attribute)
         self.class_attribute = name if class_attribute
       end
 
       def string(name, class_attribute: false)
-        attribute = Attribute.new(name.to_s, [])
+        attribute = Attribute.new_string(name)
         add_attribute(attribute)
         self.class_attribute = name if class_attribute
       end
 
       def date(name, format: 'yyyy-MM-dd HH:mm', class_attribute: false)
-        attribute = Attribute.new(name.to_s, format)
+        attribute = Attribute.new_date(name, format)
         add_attribute(attribute)
         self.class_attribute = name if class_attribute
       end
@@ -226,9 +246,26 @@ def instance_from(instance_or_values, weight:)
           instance_or_values
         else
           data = internal_values_of(instance_or_values)
+
+          # string attribute has unlimited range of possible values.
+          # Check the return index, if it is -1 then add the value to
+          # the attribute before creating the instance
+          data.map!.with_index do |value, index|
+            if value == -1 && attribute(index).string?
+              attribute(index).add_string_value(instance_or_values[index].to_s)
+            else
+              value
+            end
+          end
+
           DenseInstance.new(data, weight: weight)
         end
       end
+
+      def map_attribute_type(type)
+        return -1 unless Attribute::TYPES.include?(type.downcase.to_sym)
+        Attribute.const_get(type.upcase)
+      end
     end
 
     Java::WekaCore::Instances.__persistent__ = true

spec/classifiers/evaluation_spec.rb

@@ -27,7 +27,8 @@
       unclassified_count:             :unclassified,
       unclassified_percentage:        :pct_unclassified,
       weighted_f_measure:             :weighted_fmeasure,
-      cumulative_margin_distribution: :toCumulativeMarginDistributionString
+      cumulative_margin_distribution: :toCumulativeMarginDistributionString,
+      confusion_matrix:               :to_matrix_string
     }.each do |alias_method, method|
       it "defines the alias ##{alias_method} for ##{method}" do
         expect(subject.method(method)).to eq subject.method(alias_method)