private Tree<String> merge(Tree<String> leftTree, Tree<String> rightTree) {
int span = leftTree.getYield().size() + rightTree.getYield().size();
String mostFrequentLabel = spanToCategories.getCounter(span).argMax();
List<Tree<String>> children = new ArrayList<Tree<String>>();
children.add(leftTree);
children.add(rightTree);
return new Tree<String>(mostFrequentLabel, children);
}
private void tallyTagging(String word, String tag) {
if (!isKnown(word)) {
totalWordTypes += 1.0;
typeTagCounter.incrementCount(tag, 1.0);
}
totalTokens += 1.0;
tagCounter.incrementCount(tag, 1.0);
wordCounter.incrementCount(word, 1.0);
wordToTagCounters.incrementCount(word, tag, 1.0);
}
private int tallySpans(Tree<String> tree, int start) {
if (tree.isLeaf() || tree.isPreTerminal()) return 1;
int end = start;
for (Tree<String> child : tree.getChildren()) {
int childSpan = tallySpans(child, end);
end += childSpan;
}
String category = tree.getLabel();
if (!category.equals("ROOT")) spanToCategories.incrementCount(end - start, category, 1.0);
return end - start;
}
/* Returns a smoothed estimate of P(word|tag) */
public double scoreTagging(String word, String tag) {
double p_tag = tagCounter.getCount(tag) / totalTokens;
double c_word = wordCounter.getCount(word);
double c_tag_and_word = wordToTagCounters.getCount(word, tag);
if (c_word < 10) { // rare or unknown
c_word += 1.0;
c_tag_and_word += typeTagCounter.getCount(tag) / totalWordTypes;
}
double p_word = (1.0 + c_word) / (totalTokens + totalWordTypes);
double p_tag_given_word = c_tag_and_word / c_word;
return p_tag_given_word / p_tag * p_word;
}
