Given a span of string like [0..2) how to find string equivalent?

Question

I am using apache open nlp toolkit in java.I wish to display only name enitites in a given text like geo-graphical, person etc.. Following code snippet gives string spans

try {
        System.out.println("Input : Pierre Vinken is 61 years old");
        InputStream modelIn = new FileInputStream("en-ner-person.bin");
        TokenNameFinderModel model = new TokenNameFinderModel(modelIn);
        NameFinderME nameFinder = new NameFinderME(model);
        String[] sentence = new String[]{
                "Pierre",
                "Vinken",
                "is",
                "61",
                "years",
                "old",
                "."
                };

            Span nameSpans[] = nameFinder.find(sentence);
            for(Span s: nameSpans)
                System.out.println("Name Entity : "+s.toString());
    }
    catch (IOException e) {
      e.printStackTrace();
    }

Output :

Input : Pierre Vinken is 61 years old Name Entity : [0..2) person

How can i get the equivalent string rather than span, is there any api for that?

You have the tokenized sentence and the list indices where the name appears. Just get the relevant slice of the list of tokens and [join it](http://stackoverflow.com/questions/1751844/java-convert-liststring-to-a-joind-string). — Dan, Jan 22 '15 at 17:07
Is there any standard api to get slice ? I know I can get characters from 0 to 2 using a for loop — Akash, Jan 22 '15 at 17:30
[boon](https://github.com/boonproject/boon/wiki/Boon-Slice-Notation-for-List,-Set,-Map,-and-primitive-arrays) seems to be the way to go. — Dan, Jan 22 '15 at 23:34

score 2 · Accepted Answer · answered Jan 24 '15 at 20:59

2

Span has the method getCoveredText(CharSequence text) which will do this. But I don't understand why you need an API method to get the text corresponding to a span. A span clearly provides start (inclusive) and end (exclusive) integer offsets. So the following suffices:

StringBuilder builder = new StringBuilder();
for (int i = s.getStart(); i < s.getEnd(); i++) {
    builder.append(sentences[i]).append(" ");
}
String name = builder.toString();

answered Jan 24 '15 at 20:59

Chthonic Project

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Ya I know that. But I was expecting a direct api to obtain a string =given a string like in python I can directly get string value by string slicing . – Akash Jan 27 '15 at 16:25
In general, if I need to use a method repeatedly, and for some reason it is not there in the API, I add it to my own utility class to save myself some trouble. E.g., you could write a class called `OpenNLPUtils`, and add methods. Over the years, I've found this to be quite useful, especially for larger NLP projects. – Chthonic Project Jan 27 '15 at 19:02

score 0 · Answer 2 · answered Apr 01 '15 at 16:52

You can use the Span class itself.

The following class method returns the CharSequence that correspond to the Span instance from another CharSequence text:

/**
 * Retrieves the string covered by the current span of the specified text.
 *
 * @param text
 *
 * @return the substring covered by the current span
 */
public CharSequence getCoveredText(CharSequence text) { ... }

Notice that this class also has two static methods that accept an array of Span and respectively a CharSequence or an array of tokens (String[]) to return the equivalent array of String.

/**
 * Converts an array of {@link Span}s to an array of {@link String}s.
 *
 * @param spans
 * @param s
 * @return the strings
 */
public static String[] spansToStrings(Span[] spans, CharSequence s) {
    String[] tokens = new String[spans.length];

    for (int si = 0, sl = spans.length; si < sl; si++) {
        tokens[si] = spans[si].getCoveredText(s).toString();
    }

    return tokens;
}

public static String[] spansToStrings(Span[] spans, String[] tokens) { ... }

I hope it helps...

Given a span of string like [0..2) how to find string equivalent?

2 Answers2