DecisionRule.cs

// Accord Machine Learning Library
// The Accord.NET Framework
// http://accord-framework.net
//
// Copyright © César Souza, 2009-2017
// cesarsouza at gmail.com
//
//    This library is free software; you can redistribute it and/or
//    modify it under the terms of the GNU Lesser General Public
//    License as published by the Free Software Foundation; either
//    version 2.1 of the License, or (at your option) any later version.
//
//    This library is distributed in the hope that it will be useful,
//    but WITHOUT ANY WARRANTY; without even the implied warranty of
//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
//    Lesser General Public License for more details.
//
//    You should have received a copy of the GNU Lesser General Public
//    License along with this library; if not, write to the Free Software
//    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
//

namespace Accord.MachineLearning.DecisionTrees.Rules
{
    using System;
    using System.Collections.Generic;
    using System.Globalization;
    using System.Text;
    using Accord.Math;
    using Accord.Statistics.Filters;
    using Accord.Compat;
    using Accord.MachineLearning.DecisionTrees.Learning;

    /// <summary>
    ///   Decision Rule.
    /// </summary>
    /// 
    /// <example>
    /// <para>
    ///   The simplest way to create a set of decision rules is by extracting them from an existing <see cref="DecisionTree"/>.
    ///   The example below shows how to create a simple decision tree and convert it to a <see cref="DecisionSet">set of rules</see>
    ///   using its <see cref="DecisionTree.ToRules()"/> method.</para>
    ///   <code source="Unit Tests\Accord.Tests.MachineLearning\DecisionTrees\C45LearningTest.cs" region="doc_simplest" />
    /// </example>
    /// 
    /// <seealso cref="DecisionSet"/>
    /// <seealso cref="DecisionTree"/>
    /// <seealso cref="C45Learning"/>
    /// <seealso cref="ID3Learning"/>
    /// 
    [Serializable]
    public class DecisionRule : ICloneable, IEnumerable<Antecedent>,
        IEquatable<DecisionRule>, IComparable<DecisionRule>
    {

        private List<Antecedent> expressions;
        private DecisionVariableCollection variables;
        private double output;


        /// <summary>
        ///   Gets the decision variables handled by this rule.
        /// </summary>
        /// 
        public DecisionVariableCollection Variables { get { return variables; } }

        /// <summary>
        ///   Gets the <see cref="Antecedent"/> expressions that
        ///   must be fulfilled in order for this rule to be applicable.
        /// </summary>
        /// 
        public IList<Antecedent> Antecedents { get { return expressions; } }

        /// <summary>
        ///   Gets or sets the output of this decision rule, given 
        ///   when all <see cref="Antecedent"/> conditions are met.
        /// </summary>
        /// 
        public double Output
        {
            get { return output; }
            set { output = value; }
        }


        /// <summary>
        ///   Initializes a new instance of the <see cref="DecisionRule"/> class.
        /// </summary>
        /// 
        /// <param name="variables">The decision variables handled by this decision rule.</param>
        /// <param name="output">The output value, given after all antecedents are met.</param>
        /// <param name="antecedents">The antecedent conditions that lead to the <paramref name="output"/>.</param>
        /// 
        public DecisionRule(IList<DecisionVariable> variables,
            double output, params Antecedent[] antecedents)
            : this(variables, output, (IEnumerable<Antecedent>)antecedents)
        {
        }

        /// <summary>
        ///   Initializes a new instance of the <see cref="DecisionRule"/> class.
        /// </summary>
        /// 
        /// <param name="variables">The decision variables handled by this decision rule.</param>
        /// <param name="output">The output value, given after all antecedents are met.</param>
        /// <param name="antecedents">The antecedent conditions that lead to the <paramref name="output"/>.</param>
        /// 
        public DecisionRule(IList<DecisionVariable> variables,
            double output, IEnumerable<Antecedent> antecedents)
        {
            this.variables = new DecisionVariableCollection(variables);
            this.expressions = new List<Antecedent>(antecedents);
            this.output = output;
        }

        /// <summary>
        ///   Initializes a new instance of the <see cref="DecisionRule"/> class.
        /// </summary>
        /// 
        /// <param name="output">The output value, given after all antecedents are met.</param>
        /// <param name="antecedents">The antecedent conditions that lead to the <paramref name="output"/>.</param>
        /// 
        public DecisionRule(double output, params Antecedent[] antecedents)
        {
            this.expressions = new List<Antecedent>(antecedents);
            this.output = output;
        }

        /// <summary>
        ///   Gets the number of antecedents contained 
        ///   in this <see cref="DecisionRule"/>.
        /// </summary>
        /// 
        public int Count
        {
            get { return Antecedents.Count; }
        }

        /// <summary>
        ///   Checks whether a the rule applies to a given input vector.
        /// </summary>
        /// 
        /// <param name="input">An input vector.</param>
        /// 
        /// <returns>True, if the input matches the rule 
        ///   <see cref="Antecedents"/>; otherwise, false.
        /// </returns>
        ///   
        public bool Match(double[] input)
        {
            foreach (Antecedent expr in Antecedents)
            {
                if (!expr.Match(input))
                    return false;
            }

            return true;
        }


        /// <summary>
        ///   Creates a new <see cref="DecisionRule"/> from a <see cref="DecisionTree"/>'s
        ///   <see cref="DecisionNode"/>. This node must be a leaf, cannot be the root, and
        ///   should have one output value.
        /// </summary>
        /// 
        /// <param name="node">A <see cref="DecisionNode"/> from a <see cref="DecisionTree"/>.</param>
        /// 
        /// <returns>A <see cref="DecisionRule"/> representing the given <paramref name="node"/>.</returns>
        /// 
        public static DecisionRule FromNode(DecisionNode node)
        {
            if (node == null)
                throw new ArgumentNullException("node");

            if (!node.IsLeaf || node.IsRoot || !node.Value.HasValue)
                throw new InvalidOperationException(
                    "Only leaf nodes that have a parent can be converted to rules.");

            DecisionNode current = node;
            DecisionTree owner = current.Owner;
            double output = current.Output.Value;

            var antecedents = new List<Antecedent>();

            while (current.Parent != null)
            {
                int index = current.Parent.Branches.AttributeIndex;
                ComparisonKind comparison = current.Comparison;
                double value = current.Value.Value;

                antecedents.Insert(0, new Antecedent(index, comparison, value));

                current = current.Parent;
            }

            return new DecisionRule(node.Owner.Attributes, output, antecedents);
        }

        /// <summary>
        ///   Gets whether this rule and another rule have
        ///   the same antecedents but different outputs.
        /// </summary>
        /// 
        /// <param name="rule"></param>
        /// 
        /// <returns>True if the two rules are contradictory; 
        ///   false otherwise.</returns>
        /// 
        public bool IsInconsistentWith(DecisionRule rule)
        {
            return Antecedents.SetEquals(rule.Antecedents) && Output != rule.Output;
        }



        /// <summary>
        ///   Returns a <see cref="System.String"/> that represents this instance.
        /// </summary>
        /// 
        /// <returns>
        ///   A <see cref="System.String"/> that represents this instance.
        /// </returns>
        /// 
        public override string ToString()
        {
            return toString(null, null, System.Globalization.CultureInfo.CurrentUICulture);
        }

        /// <summary>
        ///   Returns a <see cref="System.String"/> that represents this instance.
        /// </summary>
        /// 
        /// <returns>
        ///   A <see cref="System.String"/> that represents this instance.
        /// </returns>
        /// 
        public string ToString(Codification<string> codebook)
        {
            return toString(codebook, null, System.Globalization.CultureInfo.CurrentUICulture);
        }

        /// <summary>
        ///   Returns a <see cref="System.String"/> that represents this instance.
        /// </summary>
        /// 
        /// <returns>
        ///   A <see cref="System.String"/> that represents this instance.
        /// </returns>
        /// 
        public string ToString(System.Globalization.CultureInfo cultureInfo)
        {
            return toString(null, null, cultureInfo);
        }

        /// <summary>
        ///   Returns a <see cref="System.String"/> that represents this instance.
        /// </summary>
        /// 
        /// <returns>
        ///   A <see cref="System.String"/> that represents this instance.
        /// </returns>
        /// 
        public string ToString(Codification<string> codebook, System.Globalization.CultureInfo cultureInfo)
        {
            return toString(codebook, null, cultureInfo);
        }

        /// <summary>
        ///   Returns a <see cref="System.String"/> that represents this instance.
        /// </summary>
        /// 
        /// <returns>
        ///   A <see cref="System.String"/> that represents this instance.
        /// </returns>
        /// 
        public string ToString(Codification<string> codebook, string outputColumn, System.Globalization.CultureInfo cultureInfo)
        {
            return toString(codebook, outputColumn, cultureInfo);
        }


        /// <summary>
        ///   Creates a new object that is a copy of the current instance.
        /// </summary>
        /// 
        /// <returns>
        ///   A new object that is a copy of this instance.
        /// </returns>
        /// 
        public object Clone()
        {
            return new DecisionRule(variables, output, Antecedents);
        }

        /// <summary>
        ///   Returns an enumerator that iterates through a collection.
        /// </summary>
        /// 
        /// <returns>
        ///   An <see cref="T:System.Collections.IEnumerator"/> object that 
        ///   can be used to iterate through the collection.
        /// </returns>
        /// 
        public IEnumerator<Antecedent> GetEnumerator()
        {
            return expressions.GetEnumerator();
        }

        /// <summary>
        ///   Returns an enumerator that iterates through a collection.
        /// </summary>
        /// 
        /// <returns>
        ///   An <see cref="T:System.Collections.IEnumerator"/> object that 
        ///   can be used to iterate through the collection.
        /// </returns>
        /// 
        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
        {
            return expressions.GetEnumerator();
        }

        /// <summary>
        ///   Returns a hash code for this instance.
        /// </summary>
        /// 
        /// <returns>
        ///   A hash code for this instance, suitable for use in hashing
        ///   algorithms and data structures like a hash table. 
        /// </returns>
        /// 
        public override int GetHashCode()
        {
            return this.Output.GetHashCode();
        }

        /// <summary>
        ///   Determines whether the specified <see cref="System
        ///   .Object"/> is equal to this instance.
        /// </summary>
        /// 
        /// <param name="obj">The <see cref="System.Object"/> to compare with this instance.</param>
        /// 
        /// <returns>
        ///   <c>true</c> if the specified <see cref="System.Object"/>
        ///   is equal to this instance; otherwise, <c>false</c>.
        /// </returns>
        /// 
        public override bool Equals(object obj)
        {
            return Equals(obj as DecisionRule);
        }

        /// <summary>
        ///   Determines whether the specified <see cref="DecisionRule"/> is equal to this instance.
        /// </summary>
        /// 
        /// <param name="other">The <see cref="DecisionRule"/> to compare with this instance.</param>
        /// 
        /// <returns>
        ///   <c>true</c> if the specified <see cref="DecisionRule"/>
        ///   is equal to this instance; otherwise, <c>false</c>.
        /// </returns>
        /// 
        public bool Equals(DecisionRule other)
        {
            if ((object)other == null)
                return false;

            return this.Output == other.output
              && this.Antecedents.SetEquals(other.Antecedents);
        }



        private string toString(Codification<string> codebook, string outputColumn, System.Globalization.CultureInfo culture)
        {
            StringBuilder sb = new StringBuilder();

            var expr = expressions.ToArray();

            for (int i = 0; i < expr.Length - 1; i++)
                sb.AppendFormat("({0}) && ", toString(expr[i], codebook, culture));
            sb.AppendFormat("({0})", toString(expr[expr.Length - 1], codebook, culture));

            if (String.IsNullOrEmpty(outputColumn))
                return String.Format(culture, "{0} =: {1}", Output, sb);

            string name = codebook.Revert(outputColumn, (int)Output);
            return String.Format(culture, "{0} =: {1}", name, sb);
        }

        private string toString(Antecedent antecedent, Codification<string> codebook, System.Globalization.CultureInfo culture)
        {
            int index = antecedent.Index;
            String name = Variables[index].Name;

            if (String.IsNullOrEmpty(name))
                name = "x[" + index + "]";

            String op = ComparisonExtensions.ToString(antecedent.Comparison);

            String value;
            if (codebook != null && codebook.Columns.Contains(name))
            {
                value = codebook.Revert(name, (int)antecedent.Value);
            }
            else
            {
                value = antecedent.Value.ToString(culture);
            }

            return String.Format(culture, "{0} {1} {2}", name, op, value);
        }

        /// <summary>
        ///   Compares this instance to another <see cref="DecisionRule"/>.
        /// </summary>
        /// 
        public int CompareTo(DecisionRule other)
        {
            int order = this.Output.CompareTo(other.Output);

            if (order == 0)
                return this.Antecedents.Count.CompareTo(other.Antecedents.Count);

            return order;
        }

        /// <summary>
        ///   Implements the operator &lt;.
        /// </summary>
        /// 
        public static bool operator <(DecisionRule a, DecisionRule b)
        {
            if (a.Output == b.Output)
                return a.Antecedents.Count < b.Antecedents.Count;

            return a.Output < b.Output;
        }

        /// <summary>
        ///   Implements the operator &gt;.
        /// </summary>
        /// 
        public static bool operator >(DecisionRule a, DecisionRule b)
        {
            if (a.Output == b.Output)
                return a.Antecedents.Count > b.Antecedents.Count;

            return a.Output > b.Output;
        }

        /// <summary>
        ///   Implements the operator ==.
        /// </summary>
        /// 
        public static bool operator ==(DecisionRule a, DecisionRule b)
        {
            if (System.Object.ReferenceEquals(a, b))
            {
                return true;
            }

            // If one is null, but not both, return false.
            if (((object)a == null) || ((object)b == null))
            {
                return false;
            }

            return a.Output == b.output
              && a.Antecedents.SetEquals(b.Antecedents);
        }

        /// <summary>
        ///   Implements the operator !=.
        /// </summary>
        /// 
        public static bool operator !=(DecisionRule a, DecisionRule b)
        {
            return !(a == b);
        }

    }
}