https://lucene.apache.org/lucene-parent/lucene-core: Apache Lucene Java Core (The Apache Software Foundation) 
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.lucene.search;


import java.util.Objects;

import org.apache.lucene.index.Term;
import org.apache.lucene.index.TermsEnum; // javadocs
import org.apache.lucene.util.BytesRef;

Contains statistics for a specific term


This class holds statistics for this term across all documents for scoring purposes:




The following conditions are always true:

    
  
  •  All statistics are positive integers: never zero or negative.
  
  •  docFreq <= totalTermFreq 
  •  docFreq <= sumDocFreq of the collection 
  •  totalTermFreq <= sumTotalTermFreq of the collection 



Values may include statistics on deleted documents that have not yet been merged away.

 Be careful when performing calculations on these values because they are represented as 64-bit integer values, you may need to cast to double for your use. 
@lucene.experimental
/**
 * Contains statistics for a specific term
 * <p>
 * This class holds statistics for this term across all documents for scoring purposes:
 * <ul>
 *   <li> {@link #docFreq}: number of documents this term occurs in.
 *   <li> {@link #totalTermFreq}: number of tokens for this term.
 * </ul>
 * <p>
 * The following conditions are always true:
 * <ul>
 *   <li> All statistics are positive integers: never zero or negative.
 *   <li> {@code docFreq} &lt;= {@code totalTermFreq}
 *   <li> {@code docFreq} &lt;= {@code sumDocFreq} of the collection
 *   <li> {@code totalTermFreq} &lt;= {@code sumTotalTermFreq} of the collection
 * </ul>
 * <p>
 * Values may include statistics on deleted documents that have not yet been merged away.
 * <p>
 * Be careful when performing calculations on these values because they are represented
 * as 64-bit integer values, you may need to cast to {@code double} for your use.
 * @lucene.experimental
 */
// TODO: actually add missing cross-checks to guarantee TermStatistics is in bounds of CollectionStatistics,
// otherwise many similarity functions will implode.
public class TermStatistics {
  private final BytesRef term;
  private final long docFreq;
  private final long totalTermFreq;
  
  
Creates statistics instance for a term.

Params:
  • term – Term bytes
  • docFreq – number of documents containing the term in the collection.
  • totalTermFreq – number of occurrences of the term in the collection.
Throws:
/**
   * Creates statistics instance for a term.
   * @param term Term bytes
   * @param docFreq number of documents containing the term in the collection.
   * @param totalTermFreq number of occurrences of the term in the collection.
   * @throws NullPointerException if {@code term} is {@code null}.
   * @throws IllegalArgumentException if {@code docFreq} is negative or zero.
   * @throws IllegalArgumentException if {@code totalTermFreq} is less than {@code docFreq}.
   */
  public TermStatistics(BytesRef term, long docFreq, long totalTermFreq) {
    Objects.requireNonNull(term);
    if (docFreq <= 0) {
      throw new IllegalArgumentException("docFreq must be positive, docFreq: " + docFreq);
    }
    if (totalTermFreq <= 0) {
      throw new IllegalArgumentException("totalTermFreq must be positive, totalTermFreq: " + totalTermFreq);
    }
    if (totalTermFreq < docFreq) {
      throw new IllegalArgumentException("totalTermFreq must be at least docFreq, totalTermFreq: " + totalTermFreq + ", docFreq: " + docFreq);
    }
    this.term = term;
    this.docFreq = docFreq;
    this.totalTermFreq = totalTermFreq;
  }
  
  
The term text.

 This value is never null. 
Returns:term's text, not null
/**
   * The term text.
   * <p>
   * This value is never {@code null}.
   * @return term's text, not {@code null}
   */
  public final BytesRef term() {
    return term;
  }
  
  
The number of documents this term occurs in.


This is the document-frequency for the term: the count of documents
where the term appears at least one time.

 This value is always a positive number, and never exceeds totalTermFreq. It also cannot exceed CollectionStatistics.sumDocFreq(). 
See Also:
Returns:document frequency, in the range [1 .. totalTermFreq()]
/**
   * The number of documents this term occurs in.
   * <p>
   * This is the document-frequency for the term: the count of documents
   * where the term appears at least one time.
   * <p>
   * This value is always a positive number, and never
   * exceeds {@link #totalTermFreq}. It also cannot exceed {@link CollectionStatistics#sumDocFreq()}.
   * @return document frequency, in the range [1 .. {@link #totalTermFreq()}]
   * @see TermsEnum#docFreq()
   */
  public final long docFreq() {
    return docFreq;
  }
  
  
The total number of occurrences of this term.


This is the token count for the term: the number of times it appears in the field across all documents.

 This value is always a positive number, always at least docFreq(), and never exceeds CollectionStatistics.sumTotalTermFreq(). 
See Also:
Returns:number of occurrences, in the range [docFreq() .. CollectionStatistics.sumTotalTermFreq()]
/**
   * The total number of occurrences of this term.
   * <p>
   * This is the token count for the term: the number of times it appears in the field across all documents.
   * <p>
   * This value is always a positive number, always at least {@link #docFreq()},
   * and never exceeds {@link CollectionStatistics#sumTotalTermFreq()}.
   * @return number of occurrences, in the range [{@link #docFreq()} .. {@link CollectionStatistics#sumTotalTermFreq()}]
   * @see TermsEnum#totalTermFreq()
   */
  public final long totalTermFreq() {
    return totalTermFreq;
  }
  
  @Override
  public String toString() {
    StringBuilder sb = new StringBuilder();
    sb.append("term=");
    sb.append('"');
    sb.append(Term.toString(term()));
    sb.append('"');
    sb.append(",docFreq=");
    sb.append(docFreq());
    sb.append(",totalTermFreq=");
    sb.append(totalTermFreq());
    return sb.toString();
  }
}