Question

I have a text document and a query (the query could be more than one word). I want to find the position of all occurrences of the query in the document.

I thought of the documentText.indexOf(query) or using regular expression but I could not make it work.

I end up with the following method:

First, I have create a dataType called QueryOccurrence

public class QueryOccurrence implements Serializable{
  public QueryOccurrence(){}
  private int start;
  private int end;      

  public QueryOccurrence(int nameStart,int nameEnd,String nameText){
    start=nameStart;
    end=nameEnd;        
  }

  public int getStart(){
    return start;
  }

  public int getEnd(){
    return end;
  }

  public void SetStart(int i){
    start=i;
  }

  public void SetEnd(int i){
     end=i;
  }
}

Then, I have used this datatype in the following method:

    public static List<QueryOccurrence>FindQueryPositions(String documentText, String query){

    // Normalize do the following: lower case, trim, and remove punctuation
    String normalizedQuery = Normalize.Normalize(query);
    String normalizedDocument = Normalize.Normalize(documentText);

    String[] documentWords = normalizedDocument.split(" ");;               
    String[] queryArray = normalizedQuery.split(" ");


    List<QueryOccurrence> foundQueries = new ArrayList();
    QueryOccurrence foundQuery = new QueryOccurrence();

    int index = 0;

    for (String word : documentWords) {            

        if (word.equals(queryArray[0])){
            foundQuery.SetStart(index);
        }

        if (word.equals(queryArray[queryArray.length-1])){
            foundQuery.SetEnd(index);
            if((foundQuery.End()-foundQuery.Start())+1==queryArray.length){

                //add the found query to the list
                foundQueries.add(foundQuery);
                //flush the foundQuery variable to use it again
                foundQuery= new QueryOccurrence();
            }
        }

        index++;
    }
    return foundQueries;
}

This method return a list of all occurrence of the query in the document each one with its position.

Could you suggest any easer and faster way to accomplish this task.

Thanks

Answer 1

Your first approach was a good idea, but String.indexOf does not support regular expressions.

Another easier way which uses a similar approach, but in a two step method, is as follows:

List<Integer> positions = new ArrayList();
Pattern p = Pattern.compile(queryPattern);  // insert your pattern here
Matcher m = p.matcher(documentText);
while (m.find()) {
   positions.add(m.start());
}

Where positions will hold all the start positions of the matches.