Extract the noun words & original sentence from POS Tag

Question

I want to extract the nouns from the sentence and get back the original sentence from the POS Tag

 //Extract the words before _NNP & _NN from below  and also how to get back the original sentence from the Pos TAG. 
 Original Sentence:Hi. How are you? This is Mike·
 POSTag: Hi._NNP How_WRB are_VBP you?_JJ This_DT is_VBZ Mike._NN

I tried something like this

    String txt = "Hi._NNP How_WRB are_VBP you?_JJ This_DT is_VBZ Mike._NN";


    String re1 = "((?:[a-z][a-z0-9_]*))";   // Variable Name 1
    String re2 = ".*?"; // Non-greedy match on filler
    String re3 = "(_)"; // Any Single Character 1
    String re4 = "(NNP)";   // Word 1

    Pattern p = Pattern.compile(re1 + re2 + re3 + re4, Pattern.CASE_INSENSITIVE | Pattern.DOTALL);
    Matcher m = p.matcher(txt);
    if (m.find()) {
        String var1 = m.group(1);
        System.out.print(  var1.toString()  );
    }
}

output: Hi But I need a list of all the nouns in the sentence.

Answer 1

To extract the nouns, you can do this:

public static String[] extractNouns(String sentenceWithTags) {
    // Split String into array of Strings whenever there is a tag that starts with "._NN"
    // followed by zero, one or two more letters (like "_NNP", "_NNPS", or "_NNS")
    String[] nouns = sentenceWithTags.split("_NN\\w?\\w?\\b");
    // remove all but last word (which is the noun) in every String in the array
    for(int index = 0; index < nouns.length; index++) {
        nouns[index] = nouns[index].substring(nouns[index].lastIndexOf(" ") + 1)
        // Remove all non-word characters from extracted Nouns
        .replaceAll("[^\\p{L}\\p{Nd}]", "");
    }
    return nouns;
}

To extract the original sentence, you can do this:

public static String extractOriginal(String sentenceWithTags) {
    return sentenceWithTags.replaceAll("_([A-Z]*)\\b", "");
}

Proof that it works:

public static void main(String[] args) {
    String sentence = "Hi._NNP How_WRB are_VBP you?_JJ This_DT is_VBZ Mike._NN";
    System.out.println(java.util.Arrays.toString(extractNouns(sentence)));
    System.out.println(extractOriginal(sentence));
}

Output:

[Hi, Mike]
Hi. How are you? This is Mike.

Note: for the regex that removed all non-word characters (like punctuation) from the extracted nouns, I used this Stack Overflow question/answer.