public static List<String> toTagList(List<State> states) {
List<String> tags = new ArrayList<String>();
if (states.size() > 0) {
tags.add(states.get(0).getPreviousPreviousTag());
for (State state : states) {
tags.add(state.getPreviousTag());
}
}
return tags;
}
/**
* Builds a Trellis over a sentence, by starting at the state State, and advancing through all
* legal extensions of each state already in the trellis. You should not have to modify this
* code (or even read it, really).
*/
private Trellis<State> buildTrellis(List<String> sentence) {
Trellis<State> trellis = new Trellis<State>();
trellis.setStartState(State.getStartState());
State stopState = State.getStopState(sentence.size() + 2);
trellis.setStopState(stopState);
Set<State> states = Collections.singleton(State.getStartState());
for (int position = 0; position <= sentence.size() + 1; position++) {
Set<State> nextStates = new HashSet<State>();
for (State state : states) {
if (state.equals(stopState)) continue;
LocalTrigramContext localTrigramContext =
new LocalTrigramContext(
sentence, position, state.getPreviousPreviousTag(), state.getPreviousTag());
Counter<String> tagScores = localTrigramScorer.getLogScoreCounter(localTrigramContext);
for (String tag : tagScores.keySet()) {
double score = tagScores.getCount(tag);
State nextState = state.getNextState(tag);
trellis.setTransitionCount(state, nextState, score);
nextStates.add(nextState);
}
}
// System.out.println("States: "+nextStates);
states = nextStates;
}
return trellis;
}
// to tag a sentence: build its trellis and find a path through that trellis
public List<String> tag(List<String> sentence) {
Trellis<State> trellis = buildTrellis(sentence);
List<State> states = trellisDecoder.getBestPath(trellis);
List<String> tags = State.toTagList(states);
tags = stripBoundaryTags(tags);
return tags;
}
private State(State state) {
setState(state.getPreviousPreviousTag(), state.getPreviousTag(), state.getPosition());
}
public State getPreviousState(String tag) {
return State.buildState(tag, getPreviousPreviousTag(), getPosition() - 1);
}
public State getNextState(String tag) {
return State.buildState(getPreviousTag(), tag, getPosition() + 1);
}
public static State buildState(String previousPreviousTag, String previousTag, int position) {
tempState.setState(previousPreviousTag, previousTag, position);
return stateInterner.intern(tempState);
}