source: branches/2839_HiveProjectManagement/HeuristicLab.Encodings.SymbolicExpressionTreeEncoding/3.4/ArchitectureManipulators/ArgumentDeleter.cs

#region License Information
/* HeuristicLab
 * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
 *
 * This file is part of HeuristicLab.
 *
 * HeuristicLab is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * HeuristicLab 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
 */
#endregion

using System.Linq;
using HeuristicLab.Common;
using HeuristicLab.Core;
using HeuristicLab.Data;
using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
using HeuristicLab.Random;

namespace HeuristicLab.Encodings.SymbolicExpressionTreeEncoding {
  /// <summary>
  /// As described in Koza, Bennett, Andre, Keane, Genetic Programming III - Darwinian Invention and Problem Solving, 1999, pp. 112
  /// </summary>
  [Item("ArgumentDeleter", "Manipulates a symbolic expression by deleting an argument from an existing function defining branch. As described in Koza, Bennett, Andre, Keane, Genetic Programming III - Darwinian Invention and Problem Solving, 1999, pp. 112")]
  [StorableClass]
  public sealed class ArgumentDeleter : SymbolicExpressionTreeArchitectureManipulator {
    [StorableConstructor]
    private ArgumentDeleter(bool deserializing) : base(deserializing) { }
    private ArgumentDeleter(ArgumentDeleter original, Cloner cloner) : base(original, cloner) { }
    public ArgumentDeleter() : base() { }

    public override sealed void ModifyArchitecture(
      IRandom random,
      ISymbolicExpressionTree symbolicExpressionTree,
      IntValue maxFunctionDefinitions, IntValue maxFunctionArguments) {
      DeleteArgument(random, symbolicExpressionTree, maxFunctionDefinitions.Value, maxFunctionArguments.Value);
    }

    public override IDeepCloneable Clone(Cloner cloner) {
      return new ArgumentDeleter(this, cloner);
    }

    public static bool DeleteArgument(
      IRandom random,
      ISymbolicExpressionTree symbolicExpressionTree,
      int maxFunctionDefinitions, int maxFunctionArguments) {

      var functionDefiningBranches = symbolicExpressionTree.IterateNodesPrefix().OfType<DefunTreeNode>().ToList();
      if (!functionDefiningBranches.Any())
        // no function defining branch => abort
        return false;

      var selectedDefunBranch = functionDefiningBranches.SampleRandom(random);
      if (selectedDefunBranch.NumberOfArguments <= 1)
        // argument deletion by consolidation is not possible => abort
        return false;
      // the argument to be removed is always the one with the largest index 
      // (otherwise we would have to decrement the index of the larger argument symbols)
      var removedArgument = (from sym in selectedDefunBranch.Grammar.Symbols.OfType<Argument>()
                             select sym.ArgumentIndex).Distinct().OrderBy(x => x).Last();
      // find invocations of the manipulated funcion and remove the specified argument tree
      var invocationNodes = (from node in symbolicExpressionTree.IterateNodesPrefix().OfType<InvokeFunctionTreeNode>()
                             where node.Symbol.FunctionName == selectedDefunBranch.FunctionName
                             select node).ToList();
      foreach (var invokeNode in invocationNodes) {
        invokeNode.RemoveSubtree(removedArgument);
      }

      DeleteArgumentByConsolidation(random, selectedDefunBranch, removedArgument);

      // delete the dynamic argument symbol that matches the argument to be removed
      var matchingSymbol = selectedDefunBranch.Grammar.Symbols.OfType<Argument>().Single(s => s.ArgumentIndex == removedArgument);
      selectedDefunBranch.Grammar.RemoveSymbol(matchingSymbol);
      selectedDefunBranch.NumberOfArguments--;
      // reduce arity in known functions of all root branches
      foreach (var subtree in symbolicExpressionTree.Root.Subtrees) {
        var matchingInvokeSymbol = subtree.Grammar.Symbols.OfType<InvokeFunction>().SingleOrDefault(s => s.FunctionName == selectedDefunBranch.FunctionName);
        if (matchingInvokeSymbol != null) {
          subtree.Grammar.SetSubtreeCount(matchingInvokeSymbol, selectedDefunBranch.NumberOfArguments, selectedDefunBranch.NumberOfArguments);
        }
      }
      return true;
    }

    private static void DeleteArgumentByConsolidation(IRandom random, DefunTreeNode branch, int removedArgumentIndex) {
      // replace references to the deleted argument with random references to existing arguments
      var possibleArgumentSymbols = (from sym in branch.Grammar.Symbols.OfType<Argument>()
                                     where sym.ArgumentIndex != removedArgumentIndex
                                     select sym).ToList();
      var argNodes = from node in branch.IterateNodesPrefix().OfType<ArgumentTreeNode>()
                     where node.Symbol.ArgumentIndex == removedArgumentIndex
                     select node;
      foreach (var argNode in argNodes) {
        var replacementSymbol = possibleArgumentSymbols.SampleRandom(random);
        argNode.Symbol = replacementSymbol;
      }
    }
  }
}