source: trunk/EventBenchCore/src/de/ugoe/cs/eventbench/ppm/TrieBasedModel.java @ 12

package de.ugoe.cs.eventbench.ppm;

import java.util.LinkedList;
import java.util.List;
import java.util.Random;

import de.ugoe.cs.eventbench.data.Event;
import de.ugoe.cs.eventbench.markov.IncompleteMemory;

public abstract class TrieBasedModel {

        protected int maxOrder;

        protected abstract double getProbability(List<Event<?>> context, Event<?> symbol);

        protected Trie<Event<?>> trie;
        protected final Random r;

        
        public TrieBasedModel(int maxOrder, Random r) {
                super();
                this.maxOrder = maxOrder;
                this.r = r;
        }

        public void train(List<List<Event<?>>> sequences) {
                trie = new Trie<Event<?>>();
                
                for(List<Event<?>> sequence : sequences) {
                        List<Event<?>> currentSequence = new LinkedList<Event<?>>(sequence); // defensive copy
                        currentSequence.add(0, Event.STARTEVENT);
                        currentSequence.add(Event.ENDEVENT);
                        
                        trie.train(currentSequence, maxOrder);
                }
        }

        public List<? extends Event<?>> randomSequence() {
                List<Event<?>> sequence = new LinkedList<Event<?>>();
                
                IncompleteMemory<Event<?>> context = new IncompleteMemory<Event<?>>(maxOrder-1);
                context.add(Event.STARTEVENT);
                
                Event<?> currentState = Event.STARTEVENT;
                
                boolean endFound = false;
                
                while(!endFound) {
                        double randVal = r.nextDouble();
                        double probSum = 0.0;
                        List<Event<?>> currentContext = context.getLast(maxOrder);
                        for( Event<?> symbol : trie.getKnownSymbols() ) {
                                probSum += getProbability(currentContext, symbol);
                                if( probSum>=randVal ) {
                                        endFound = (symbol==Event.ENDEVENT);
                                        if( !(symbol==Event.STARTEVENT || symbol==Event.ENDEVENT) ) {
                                                // only add the symbol the sequence if it is not START or END
                                                context.add(symbol);
                                                currentState = symbol;
                                                sequence.add(currentState);
                                        }
                                        break;
                                }
                        }
                }
                return sequence;
        }

        @Override
        public String toString() {
                return trie.toString();
        }

}