CODEWITHSUNDEEP
javanlpstanford-nlpjgrapht
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Tex

Reputation: 950

Get certain nodes out of a Parse Tree

I am working on a project involving anaphora resolution via Hobbs algorithm. I have parsed my text using the Stanford parser, and now I would like to manipulate the nodes in order to implement my algorithm.

At the moment, I don't understand how to:

Upvotes: 3

Views: 6009

Answers (2)

Christopher Manning
Christopher Manning

Reputation: 9450

@dhg's answer works fine, but here are two other options that it might also be useful to know about:

  • The Tree class implements Iterable. You can iterate through all the nodes of a Tree, or, strictly, the subtrees headed by each node, in a pre-order traversal, with:

    for (Tree subtree : t) { 
    if (subtree.label().value().equals("PRP")) {
        pronouns.add(subtree);
    }
}

  • You can also get just nodes that satisfy some (potentially quite complex pattern) by using tregex, which behaves rather like java.util.regex by allowing pattern matches over trees. You would have something like:

    TregexPattern tgrepPattern = TregexPattern.compile("PRP");
TregexMatcher m = tgrepPattern.matcher(t);
while (m.find()) {
    Tree subtree = m.getMatch();
    pronouns.add(subtree);
}

Upvotes: 10

dhg
dhg

Reputation: 52691

Here's a simple example that parses a sentence and finds all of the pronouns.

private static ArrayList<Tree> findPro(Tree t) {
    ArrayList<Tree> pronouns = new ArrayList<Tree>();
    if (t.label().value().equals("PRP"))
        pronouns.add(t);
    else
        for (Tree child : t.children())
            pronouns.addAll(findPro(child));
    return pronouns;
}

public static void main(String[] args) {

    LexicalizedParser parser = LexicalizedParser.loadModel();
    Tree x = parser.apply("The dog walks and he barks .");
    System.out.println(x);
    ArrayList<Tree> pronouns = findPro(x);
    System.out.println("All Pronouns: " + pronouns);

}

This prints:

    (ROOT (S (S (NP (DT The) (NN dog)) (VP (VBZ walks))) (CC and) (S (NP (PRP he)) (VP (VBZ barks))) (. .)))
    All Pronouns: [(PRP he)]

Upvotes: 5

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