/// <summary>
/// Creates a new sequence of outcomes by cloning an existing sequence.
/// </summary>
/// <param name="sequenceToCopy">
/// The sequence to create the clone from.
/// </param>
public Sequence(Sequence sequenceToCopy)
{
_outcomes = new List<string>(sequenceToCopy.Outcomes.Count + 1);
_outcomes.AddRange(sequenceToCopy.Outcomes);
_probabilities = new List<double>(sequenceToCopy.Probabilities.Count + 1);
_probabilities.AddRange(sequenceToCopy.Probabilities);
_score = sequenceToCopy.Score;
}
/// <summary>
/// Determines whether a particular continuation of a sequence is valid.
/// This is used to restrict invalid sequences such as thoses used in start/continue tag-based chunking
/// or could be used to implement tag dictionary restrictions.
/// </summary>
/// <param name="index">
/// The index in the input sequence for which the new outcome is being proposed.
/// </param>
/// <param name="inputSequence">
/// The input sequnce.
/// </param>
/// <param name="outcomesSequence">
/// The outcomes so far in this sequence.
/// </param>
/// <param name="outcome">
/// The next proposed outcome for the outcomes sequence.
/// </param>
/// <returns>
/// true if the sequence would still be valid with the new outcome, false otherwise.
/// </returns>
protected internal virtual bool ValidSequence(int index, ArrayList inputSequence, Sequence outcomesSequence, string outcome)
{
return true;
}
/// <summary>
/// Returns the best sequence of outcomes based on model for this object.</summary>
/// <param name="numSequences">
/// The maximum number of sequences to be returned.
/// </param>
/// <param name="sequence">
/// The input sequence.
/// </param>
/// <param name="additionalContext">
/// An object[] of additional context. This is passed to the context generator blindly with the assumption that the context are appropiate.
/// </param>
/// <param name="minSequenceScore">
/// A lower bound on the score of a returned sequence.</param>
/// <returns>
/// An array of the top ranked sequences of outcomes.
/// </returns>
public virtual Sequence[] BestSequences(int numSequences, object[] sequence, object[] additionalContext, double minSequenceScore)
{
int sequenceCount = sequence.Length;
ListHeap<Sequence> previousHeap = new ListHeap<Sequence>(Size);
ListHeap<Sequence> nextHeap = new ListHeap<Sequence>(Size);
ListHeap<Sequence> tempHeap;
previousHeap.Add(new Sequence());
if (additionalContext == null)
{
additionalContext = mEmptyAdditionalContext;
}
for (int currentSequence = 0; currentSequence < sequenceCount; currentSequence++)
{
int sz = System.Math.Min(Size, previousHeap.Size);
int sc = 0;
for (; previousHeap.Size > 0 && sc < sz; sc++)
{
Sequence topSequence = previousHeap.Extract();
String[] outcomes = topSequence.Outcomes.ToArray();
String[] contexts = ContextGenerator.GetContext(currentSequence, sequence, outcomes, additionalContext);
double[] scores;
if (mContextsCache != null)
{
scores = (double[]) mContextsCache[contexts];
if (scores == null)
{
scores = Model.Evaluate(contexts, mProbabilities);
mContextsCache[contexts] = scores;
}
}
else
{
scores = Model.Evaluate(contexts, mProbabilities);
}
double[] tempScores = new double[scores.Length];
Array.Copy(scores, tempScores, scores.Length);
Array.Sort(tempScores);
double minimum = tempScores[System.Math.Max(0, scores.Length - Size)];
for (int currentScore = 0; currentScore < scores.Length; currentScore++)
{
if (scores[currentScore] < minimum)
{
continue; //only advance first "size" outcomes
}
string outcomeName = Model.GetOutcomeName(currentScore);
if (ValidSequence(currentSequence, sequence, outcomes, outcomeName))
{
Sequence newSequence = new Sequence(topSequence, outcomeName, scores[currentScore]);
if (newSequence.Score > minSequenceScore)
{
nextHeap.Add(newSequence);
}
}
}
if (nextHeap.Size == 0)
{//if no advanced sequences, advance all valid
for (int currentScore = 0; currentScore < scores.Length; currentScore++)
{
string outcomeName = Model.GetOutcomeName(currentScore);
if (ValidSequence(currentSequence, sequence, outcomes, outcomeName))
{
Sequence newSequence = new Sequence(topSequence, outcomeName, scores[currentScore]);
if (newSequence.Score > minSequenceScore)
{
nextHeap.Add(newSequence);
}
}
}
}
//nextHeap.Sort();
}
// make prev = next; and re-init next (we reuse existing prev set once we clear it)
previousHeap.Clear();
tempHeap = previousHeap;
previousHeap = nextHeap;
nextHeap = tempHeap;
}
int topSequenceCount = System.Math.Min(numSequences, previousHeap.Size);
Sequence[] topSequences = new Sequence[topSequenceCount];
int sequenceIndex = 0;
for (; sequenceIndex < topSequenceCount; sequenceIndex++)
{
topSequences[sequenceIndex] = (Sequence) previousHeap.Extract();
}
return topSequences;
}
public virtual string[] GetContext(int index, List<string> sequence, Sequence outcomesSequence, object[] additionalContext)
{
return GetContext(index, sequence, outcomesSequence.Outcomes, (IDictionary<string, string>) additionalContext[0]);
}
protected internal override bool ValidSequence(int index, ArrayList sequence, Sequence outcomeSequence, string outcome)
{
return mNameFinder.ValidOutcome(outcome, outcomeSequence);
}
/// <summary>
/// This method determines wheter the outcome is valid for the preceding sequence.
/// This can be used to implement constraints on what sequences are valid.
/// </summary>
/// <param name="outcome">
/// The outcome.
/// </param>
/// <param name="sequence">
/// The preceding sequence of outcome assignments.
/// </param>
/// <returns>
/// true is the outcome is valid for the sequence, false otherwise.
/// </returns>
protected internal virtual bool ValidOutcome(string outcome, Sequence sequence)
{
if (outcome == Continue)
{
string[] tags = sequence.Outcomes.ToArray();
int lastTag = tags.Length - 1;
if (lastTag == -1)
{
return false;
}
else if (tags[lastTag] == Other)
{
return false;
}
}
return true;
}
public virtual string[] Find(object[] tokens, IDictionary previousTags)
{
mBestSequence = mBeam.BestSequence(tokens, new object[]{previousTags});
ArrayList outcomes = new ArrayList(mBestSequence.Outcomes);
return (string[]) outcomes.ToArray(typeof(string));
}
public virtual ArrayList Find(ArrayList tokens, IDictionary previousTags)
{
mBestSequence = mBeam.BestSequence(tokens, new object[]{previousTags});
return new ArrayList(mBestSequence.Outcomes);
}
/// <summary>
/// Creates a new sequence of outcomes based on an existing sequence.
/// </summary>
/// <param name="sequenceToCopy">
/// The sequence to base the new sequence on.
/// </param>
/// <param name="outcome">
/// An additional outcome to add onto the sequence.
/// </param>
/// <param name="probability">
/// An existing probability to add onto the sequence.
/// </param>
public Sequence(Sequence sequenceToCopy, string outcome, double probability)
{
_outcomes = new List<string>(sequenceToCopy.Outcomes.Count + 1);
_outcomes.AddRange(sequenceToCopy.Outcomes);
_outcomes.Add(outcome);
_probabilities = new List<double>(sequenceToCopy.Probabilities.Count + 1);
_probabilities.AddRange(sequenceToCopy.Probabilities);
_probabilities.Add(probability);
_score = sequenceToCopy.Score + System.Math.Log(probability);
}
// Methods --------------------------
public virtual string[] Find(string[] tokens, IDictionary previousTags)
{
mBestSequence = mBeam.BestSequence(tokens, new object[]{previousTags});
return mBestSequence.Outcomes.ToArray();
}