Package org.apache.lucene.classification

# Class KNearestNeighborClassifier

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

All Implemented Interfaces:
  `Classifier<BytesRef>`

Direct Known Subclasses:
  `KNearestNeighborDocumentClassifier`

public class KNearestNeighborClassifier extends Object implements Classifier<BytesRef>
A k-Nearest Neighbor classifier (see `http://en.wikipedia.org/wiki/K-nearest_neighbors` ) based on `MoreLikeThis`

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

## Field Summary

Fields
Modifier and Type
Field
Description
`protected final String`
`classFieldName`
the name of the field used as the output text
`protected final IndexSearcher`
`indexSearcher`
an `IndexSearcher` used to perform queries
`protected final int`
`k`
the no.
`protected final MoreLikeThis`
`mlt`
a `MoreLikeThis` instance used to perform MLT queries
`protected final Query`
`query`
a `Query` used to filter the documents that should be used from this classifier's underlying `LeafReader`
`protected final String[]`
`textFieldNames`
the name of the fields used as the input text

## Constructor Summary

Constructors
Constructor
Description
`KNearestNeighborClassifier(IndexReader indexReader, Similarity similarity, Analyzer analyzer, Query query, int k, int minDocsFreq, int minTermFreq, String classFieldName, String... textFieldNames)`
Creates a `KNearestNeighborClassifier`.

## Method Summary

Modifier and Type
Method
Description
`ClassificationResult<BytesRef>`
`assignClass(String text)`
Assign a class (with score) to the given text String
`protected List<ClassificationResult<BytesRef>>`
`buildListFromTopDocs(TopDocs topDocs)`
build a list of classification results from search results
`protected ClassificationResult<BytesRef>`
`classifyFromTopDocs(TopDocs knnResults)`
TODO
`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.
`String`
`toString()`

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

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

## Field Details

### mlt

protected final MoreLikeThis mlt
a `MoreLikeThis` instance used to perform MLT queries

### textFieldNames

protected final String[] textFieldNames
the name of the fields used as the input text

### classFieldName

protected final String classFieldName
the name of the field used as the output text

### indexSearcher

protected final IndexSearcher indexSearcher
an `IndexSearcher` used to perform queries

### k

protected final int k
the no. of docs to compare in order to find the nearest neighbor to the input text

### query

protected final Query query
a `Query` used to filter the documents that should be used from this classifier's underlying `LeafReader`

## Constructor Details

### KNearestNeighborClassifier

public KNearestNeighborClassifier(IndexReader indexReader, Similarity similarity, Analyzer analyzer, Query query, int k, int minDocsFreq, int minTermFreq, String classFieldName, String... textFieldNames) throws IOException
Creates a `KNearestNeighborClassifier`.

Parameters:
  `indexReader` - the reader on the index to be used for classification
  `similarity` - the `Similarity` to be used by the underlying `IndexSearcher` or `null` (defaults to `BM25Similarity`)
  `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
  `k` - the no. of docs to select in the MLT results to find the nearest neighbor
  `minDocsFreq` - `MoreLikeThis.minDocFreq` parameter
  `minTermFreq` - `MoreLikeThis.minTermFreq` parameter
  `classFieldName` - the name of the field used as the output for the classifier
  `textFieldNames` - the name of the fields used as the inputs for the classifier, they can contain boosting indication e.g. title^10
Throws:
  `IOException`

## Method Details

### assignClass

public ClassificationResult<BytesRef> assignClass(String text) 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:
  `text` - 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.

### classifyFromTopDocs

protected ClassificationResult<BytesRef> classifyFromTopDocs(TopDocs knnResults) throws IOException
TODO

Throws:
  `IOException`

### 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.

### buildListFromTopDocs

protected List<ClassificationResult<BytesRef>> buildListFromTopDocs(TopDocs topDocs) throws IOException
build a list of classification results from search results

Parameters:
  `topDocs` - the search results as a `TopDocs` object
Returns:
  a `List` of `ClassificationResult`, one for each existing class
Throws:
  `IOException` - if it's not possible to get the stored value of class field

### toString

public String toString()

Overrides:
  `toString` in class `Object`