Package org.apache.lucene.classification

# Class BM25NBClassifier

java.lang.Object
org.apache.lucene.classification.BM25NBClassifier

All Implemented Interfaces:
  `Classifier<BytesRef>`

public class BM25NBClassifier extends Object implements Classifier<BytesRef>
A classifier approximating naive bayes classifier by using pure queries on BM25.

WARNING: This API is experimental and might change in incompatible ways in the next release.

## Constructor Summary

Constructors
Constructor
Description
`BM25NBClassifier(IndexReader indexReader, Analyzer analyzer, Query query, String classFieldName, String... textFieldNames)`
Creates a new NaiveBayes classifier.

## Method Summary

Modifier and Type
Method
Description
`ClassificationResult<BytesRef>`
`assignClass(String inputDocument)`
Assign a class (with score) to the given text String
`List<ClassificationResult<BytesRef>>`
`getClasses(String text)`
Get all the classes (sorted by score, descending) assigned to the given text String.
`List<ClassificationResult<BytesRef>>`
`getClasses(String text, int max)`
Get the first `max` classes (sorted by score, descending) assigned to the given text String.

### Methods inherited from class java.lang.Object

`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

## Constructor Details

### BM25NBClassifier

public BM25NBClassifier(IndexReader indexReader, Analyzer analyzer, Query query, String classFieldName, String... textFieldNames)
Creates a new NaiveBayes classifier.

Parameters:
  `indexReader` - the reader on the index to be used for classification
  `analyzer` - an `Analyzer` used to analyze unseen text
  `query` - a `Query` to eventually filter the docs used for training the classifier, or `null` if all the indexed docs should be used
  `classFieldName` - the name of the field used as the output for the classifier NOTE: must not be heavely analyzed as the returned class will be a token indexed for this field
  `textFieldNames` - the name of the fields used as the inputs for the classifier, NO boosting supported per field

## Method Details

### assignClass

public ClassificationResult<BytesRef> assignClass(String inputDocument) throws IOException
Description copied from interface: `Classifier`
Assign a class (with score) to the given text String

Specified by:
  `assignClass` in interface `Classifier<BytesRef>`
Parameters:
  `inputDocument` - a String containing text to be classified
Returns:
  a `ClassificationResult` holding assigned class of type `T` and score
Throws:
  `IOException` - If there is a low-level I/O error.

### getClasses

public List<ClassificationResult<BytesRef>> getClasses(String text) throws IOException
Description copied from interface: `Classifier`
Get all the classes (sorted by score, descending) assigned to the given text String.

Specified by:
  `getClasses` in interface `Classifier<BytesRef>`
Parameters:
  `text` - a String containing text to be classified
Returns:
  the whole list of `ClassificationResult`, the classes and scores. Returns `null` if the classifier can't make lists.
Throws:
  `IOException` - If there is a low-level I/O error.

### getClasses

public List<ClassificationResult<BytesRef>> getClasses(String text, int max) throws IOException
Description copied from interface: `Classifier`
Get the first `max` classes (sorted by score, descending) assigned to the given text String.

Specified by:
  `getClasses` in interface `Classifier<BytesRef>`
Parameters:
  `text` - a String containing text to be classified
  `max` - the number of return list elements
Returns:
  the whole list of `ClassificationResult`, the classes and scores. Cut for "max" number of elements. Returns `null` if the classifier can't make lists.
Throws:
  `IOException` - If there is a low-level I/O error.