https://lucene.apache.org/lucene-parent/lucene-core: Apache Lucene Java Core (The Apache Software Foundation) 
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 * 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.
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package org.apache.lucene.search;

import java.util.Objects;

import org.apache.lucene.index.IndexReader; // javadocs
import org.apache.lucene.index.Terms;       // javadocs



Contains statistics for a collection (field).


This class holds statistics across all documents for scoring purposes:




The following conditions are always true:

    
  
  •  All statistics are positive integers: never zero or negative.
  
  •  docCount <= maxDoc 
  •  docCount <= sumDocFreq <= sumTotalTermFreq 



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 collection (field).
 * <p>
 * This class holds statistics across all documents for scoring purposes:
 * <ul>
 *   <li> {@link #maxDoc()}: number of documents.
 *   <li> {@link #docCount()}: number of documents that contain this field.
 *   <li> {@link #sumDocFreq()}: number of postings-list entries.
 *   <li> {@link #sumTotalTermFreq()}: number of tokens.
 * </ul>
 * <p>
 * The following conditions are always true:
 * <ul>
 *   <li> All statistics are positive integers: never zero or negative.
 *   <li> {@code docCount} &lt;= {@code maxDoc}
 *   <li> {@code docCount} &lt;= {@code sumDocFreq} &lt;= {@code sumTotalTermFreq}
 * </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
 */
public class CollectionStatistics {
  private final String field;
  private final long maxDoc;
  private final long docCount;
  private final long sumTotalTermFreq;
  private final long sumDocFreq;
  
  
Creates statistics instance for a collection (field).

Params:
  • field – Field's name
  • maxDoc – total number of documents.
  • docCount – number of documents containing the field.
  • sumTotalTermFreq – number of tokens in the field.
  • sumDocFreq – number of postings list entries for the field.
Throws:
/**
   * Creates statistics instance for a collection (field).
   * @param field Field's name
   * @param maxDoc total number of documents.
   * @param docCount number of documents containing the field.
   * @param sumTotalTermFreq number of tokens in the field.
   * @param sumDocFreq number of postings list entries for the field.
   * @throws IllegalArgumentException if {@code maxDoc} is negative or zero.
   * @throws IllegalArgumentException if {@code docCount} is negative or zero.
   * @throws IllegalArgumentException if {@code docCount} is more than {@code maxDoc}.
   * @throws IllegalArgumentException if {@code sumDocFreq} is less than {@code docCount}.
   * @throws IllegalArgumentException if {@code sumTotalTermFreq} is less than {@code sumDocFreq}.
   */
  public CollectionStatistics(String field, long maxDoc, long docCount, long sumTotalTermFreq, long sumDocFreq) {
    Objects.requireNonNull(field);
    if (maxDoc <= 0) {
      throw new IllegalArgumentException("maxDoc must be positive, maxDoc: " + maxDoc);
    }
    if (docCount <= 0) {
      throw new IllegalArgumentException("docCount must be positive, docCount: " + docCount);
    }
    if (docCount > maxDoc) {
      throw new IllegalArgumentException("docCount must not exceed maxDoc, docCount: " + docCount + ", maxDoc: " + maxDoc);
    }
    if (sumDocFreq <= 0) {
      throw new IllegalArgumentException("sumDocFreq must be positive, sumDocFreq: " + sumDocFreq);
    }
    if (sumDocFreq < docCount) {
      throw new IllegalArgumentException("sumDocFreq must be at least docCount, sumDocFreq: " + sumDocFreq + ", docCount: " + docCount);
    }
    if (sumTotalTermFreq <= 0) {
      throw new IllegalArgumentException("sumTotalTermFreq must be positive, sumTotalTermFreq: " + sumTotalTermFreq);
    }
    if (sumTotalTermFreq < sumDocFreq) {
      throw new IllegalArgumentException("sumTotalTermFreq must be at least sumDocFreq, sumTotalTermFreq: " + sumTotalTermFreq + ", sumDocFreq: " + sumDocFreq);
    }
    this.field = field;
    this.maxDoc = maxDoc;
    this.docCount = docCount;
    this.sumTotalTermFreq = sumTotalTermFreq;
    this.sumDocFreq = sumDocFreq;
  }
  
  
The field's name.

 This value is never null. 
Returns:field's name, not null
/**
   * The field's name.
   * <p>
   * This value is never {@code null}.
   * @return field's name, not {@code null}
   */
  public final String field() {
    return field;
  }
  
  
The total number of documents, regardless of
whether they all contain values for this field.


This value is always a positive number.

See Also:
Returns:total number of documents, in the range [1 .. Long.MAX_VALUE]
/**
   * The total number of documents, regardless of
   * whether they all contain values for this field.
   * <p>
   * This value is always a positive number.
   * @return total number of documents, in the range [1 .. {@link Long#MAX_VALUE}]
   * @see IndexReader#maxDoc()
   */
  public final long maxDoc() {
    return maxDoc;
  }
  
  
The total number of documents that have at least
one term for this field.

 This value is always a positive number, and never exceeds maxDoc(). 
See Also:
Returns:total number of documents containing this field, in the range [1 .. maxDoc()]
/**
   * The total number of documents that have at least
   * one term for this field.
   * <p>
   * This value is always a positive number, and never
   * exceeds {@link #maxDoc()}.
   * @return total number of documents containing this field, in the range [1 .. {@link #maxDoc()}]
   * @see Terms#getDocCount()
   */
  public final long docCount() {
    return docCount;
  }
  
  
The total number of tokens for this field. This is the "word count" for this field across all documents. It is the sum of TermStatistics.totalTermFreq() across all terms. It is also the sum of each document's field length across all documents. 
 This value is always a positive number, and always at least sumDocFreq(). 
See Also:
Returns:total number of tokens in the field, in the range [sumDocFreq() .. Long.MAX_VALUE]
/**
   * The total number of tokens for this field.
   * This is the "word count" for this field across all documents.
   * It is the sum of {@link TermStatistics#totalTermFreq()} across all terms.
   * It is also the sum of each document's field length across all documents.
   * <p>
   * This value is always a positive number, and always at least {@link #sumDocFreq()}.
   * @return total number of tokens in the field, in the range [{@link #sumDocFreq()} .. {@link Long#MAX_VALUE}]
   * @see Terms#getSumTotalTermFreq()
   */
  public final long sumTotalTermFreq() {
    return sumTotalTermFreq;
  }
  
  
The total number of posting list entries for this field. This is the sum of term-document pairs: the sum of TermStatistics.docFreq() across all terms. It is also the sum of each document's unique term count for this field across all documents. 
 This value is always a positive number, always at least docCount(), and never exceeds sumTotalTermFreq(). 
See Also:
Returns:number of posting list entries, in the range [docCount() .. sumTotalTermFreq()]
/**
   * The total number of posting list entries for this field.
   * This is the sum of term-document pairs: the sum of {@link TermStatistics#docFreq()} across all terms.
   * It is also the sum of each document's unique term count for this field across all documents.
   * <p>
   * This value is always a positive number, always at least {@link #docCount()}, and never
   * exceeds {@link #sumTotalTermFreq()}.
   * @return number of posting list entries, in the range [{@link #docCount()} .. {@link #sumTotalTermFreq()}]
   * @see Terms#getSumDocFreq()
   */
  public final long sumDocFreq() {
    return sumDocFreq;
  }

  @Override
  public String toString() {
    StringBuilder sb = new StringBuilder();
    sb.append("field=");
    sb.append('"');
    sb.append(field());
    sb.append('"');
    sb.append(",maxDoc=");
    sb.append(maxDoc());
    sb.append(",docCount=");
    sb.append(docCount());
    sb.append(",sumTotalTermFreq=");
    sb.append(sumTotalTermFreq());
    sb.append(",sumDocFreq=");
    sb.append(sumDocFreq);
    return sb.toString();
  }
}