How to get the Stanford parser output as a list of nodes and edges?

Question

I'm processing a batch of text files, and I need to use the Stanford parser's output as a numeric list of nodes and edges where Nodes have IDs and labels, edges consist of two node ids and an edge weight like:

Node List:   1  A ,  2  B...
Edge list:  1 2 10, 2 1 10...

According to the Stanford NLP javadoc -->Class SemanticGraph:

There is no mechanism for returning all edges at once (eg edgeSet()). This is intentional. Use edgeIterable() to iterate over the edges if necessary.

How to do it? I tried this code:

import java.io.*;
import java.util.*;

import edu.stanford.nlp.io.*;
import edu.stanford.nlp.ling.*;
import edu.stanford.nlp.pipeline.*;
import edu.stanford.nlp.semgraph.SemanticGraph;
import edu.stanford.nlp.semgraph.SemanticGraphEdge;
import edu.stanford.nlp.trees.*;
import edu.stanford.nlp.util.*;

public class StanfordCoreNlpSemGraph {
  public static void main(String[] args) throws IOException {
    PrintWriter out;
    if (args.length > 1) {
      out = new PrintWriter(args[1]);
    } else {
      out = new PrintWriter(System.out);
    }
    PrintWriter xmlOut = null;
    if (args.length > 2) {
      xmlOut = new PrintWriter(args[2]);
    }

    StanfordCoreNLP pipeline = new StanfordCoreNLP();
    Annotation annotation;
    if (args.length > 0) {
      annotation = new Annotation(IOUtils.slurpFileNoExceptions(args[0]));
    } else {
      annotation = new Annotation("This is the first annotation.");
    }

    pipeline.annotate(annotation);
    pipeline.prettyPrint(annotation, out);
    if (xmlOut != null) {
      pipeline.xmlPrint(annotation, xmlOut);
    }
      // An Annotation is a Map.
     // For instance, this gets the parse tree of the first sentence. 

    List<CoreMap> sentences = annotation.get(CoreAnnotations.SentencesAnnotation.class);
    if (sentences != null && sentences.size() > 0) {
      CoreMap sentence = sentences.get(0);
      Tree tree = sentence.get(TreeCoreAnnotations.TreeAnnotation.class);
      out.println();
      out.println("The first sentence parsed is:");
      tree.pennPrint(out);
      Object IndexedWord;
      SemanticGraph sg = new SemanticGraph();

      SemanticGraphEdge edge = new SemanticGraphEdge(edge);

      for (SemanticGraphEdge edge : sg.edgeIterable()) 
      {
        int headIndex = edge.getGovernor().index();
        int depIndex = edge.getDependent().index();
        int weight = 1; // "edge weight"-- should it be the 
        // sum of the weights of the 
        // selected edges? 
        System.out.printf("%d %d %d%n", headIndex, depIndex, weight);
      }  
    }
  }
}

But it throws an error: Duplicate local variable edge StanfordCoreNlpSemGraph.java /stan-nlp/src line 60

Answer 1

Here's a basic example of forming the edge list. (The node list part should be easy — you just need to iterate over the tokens in the sentence and print them out.)

SemanticGraph sg = ....
for (SemanticGraphEdge edge : sg.getEdgesIterable()) {
  int headIndex = edge.getGovernor().index();
  int depIndex = edge.getDependent().index();
  int weight = ... // Not sure what "edge weight" you want here.
  System.out.printf("%d %d %d%n", headIndex, depIndex, weight);
}