PrimitiveSetImpl.java

/*
 * Copyright 2015 S. Webber
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.oakgp.primitive;

import java.util.List;

import org.oakgp.Type;
import org.oakgp.function.Function;
import org.oakgp.function.Signature;
import org.oakgp.node.Node;
import org.oakgp.util.Random;

/** Represents the range of possible functions and terminal nodes to use during a genetic programming run. */
public final class PrimitiveSetImpl implements PrimitiveSet {
   private final FunctionSet functionSet;
   private final ConstantSet constantSet;
   private final VariableSet variableSet;
   private final Random random;
   private final double ratioVariables;

   /**
    * Constructs a new primitive set consisting of the specified components.
    *
    * @param functionSet
    *           the set of possible functions to use in the construction of programs
    * @param constantSet
    *           the set of possible constants to use in the construction of programs
    * @param variableSet
    *           the set of possible variables to use in the construction of programs
    * @param random
    *           used to randomly select components to use in the construction of programs
    * @param ratioVariables
    *           a value in the range 0 to 1 (inclusive) which specifies the proportion of terminal nodes that should represent variables, rather than constants
    */
   public PrimitiveSetImpl(FunctionSet functionSet, ConstantSet constantSet, VariableSet variableSet, Random random, double ratioVariables) {
      this.functionSet = functionSet;
      this.constantSet = constantSet;
      this.variableSet = variableSet;
      this.random = random;
      this.ratioVariables = ratioVariables;
   }

   @Override
   public boolean hasTerminals(Type type) {
      return variableSet.getByType(type) != null || constantSet.getByType(type) != null;
   }

   @Override
   public boolean hasFunctions(Type type) {
      return functionSet.getByType(type) != null;
   }

   /**
    * Returns a randomly selected terminal node.
    *
    * @return a randomly selected terminal node
    */
   @Override
   public Node nextTerminal(Type type) {
      boolean doCreateVariable = doCreateVariable();
      Node next = nextTerminal(type, doCreateVariable);
      if (next == null) {
         next = nextTerminal(type, !doCreateVariable);
      }
      if (next == null) {
         throw new IllegalArgumentException("No terminals of type: " + type);
      } else {
         return next;
      }
   }

   private Node nextTerminal(Type type, boolean doCreateVariable) {
      List<? extends Node> possibilities = doCreateVariable ? variableSet.getByType(type) : constantSet.getByType(type);
      return randomlySelectAlternative(null, possibilities);
   }

   /**
    * Returns a randomly selected terminal node that is not the same as the specified {@code Node}.
    *
    * @param current
    *           the current {@code Node} that the returned result should be an alternative to (i.e. not the same as)
    * @return a randomly selected terminal node that is not the same as the specified {@code Node}
    */
   @Override
   public Node nextAlternativeTerminal(Node current) {
      boolean doCreateVariable = doCreateVariable();
      Node next = nextAlternativeNode(current, doCreateVariable);
      if (next == current) {
         return nextAlternativeNode(current, !doCreateVariable);
      } else {
         return next;
      }
   }

   private boolean doCreateVariable() {
      return random.nextDouble() < ratioVariables;
   }

   private Node nextAlternativeNode(Node current, boolean doCreateVariable) {
      Type type = current.getType();
      List<? extends Node> possibilities = doCreateVariable ? variableSet.getByType(type) : constantSet.getByType(type);
      return randomlySelectAlternative(current, possibilities);
   }

   /**
    * Returns a randomly selected {@code Function} of the specified {@code Type}.
    *
    * @param type
    *           the required return type of the {@code Function}
    * @return a randomly selected {@code Function} with a return type of {@code type}
    */
   @Override
   public Function nextFunction(Type type) {
      List<Function> typeFunctions = functionSet.getByType(type);
      if (typeFunctions == null) {
         throw new IllegalArgumentException("No functions with return type: " + type);
      }
      int index = nextInt(typeFunctions.size());
      return typeFunctions.get(index);
   }

   /**
    * Returns a randomly selected {@code Function} that is not the same as the specified {@code Function}.
    *
    * @param current
    *           the current {@code Function} that the returned result should be an alternative to (i.e. not the same as)
    * @return a randomly selected {@code Function} that is not the same as the specified {@code Function}
    */
   @Override
   public Function nextAlternativeFunction(Function current) {
      Signature signature = current.getSignature();
      List<Function> functions = functionSet.getBySignature(signature);
      return randomlySelectAlternative(current, functions);
   }

   private <C, P extends C> C randomlySelectAlternative(C currentVersion, List<P> possibilities) {
      if (possibilities == null) {
         return currentVersion;
      }

      int possibilitiesSize = possibilities.size();
      int randomIndex = nextInt(possibilitiesSize);
      C next = possibilities.get(randomIndex);
      if (next == currentVersion) {
         if (possibilitiesSize == 1) {
            return currentVersion;
         }

         int secondRandomIndex = nextInt(possibilitiesSize - 1);
         if (secondRandomIndex >= randomIndex) {
            return possibilities.get(secondRandomIndex + 1);
         } else {
            return possibilities.get(secondRandomIndex);
         }
      } else {
         return next;
      }
   }

   private int nextInt(int bound) {
      return bound == 1 ? 0 : random.nextInt(bound);
   }
}