[GitHub] [lucene] gsmiller commented on a change in pull request #133: LUCENE-9950: New facet counting implementation for general string doc value fields

[GitBox <gi...@apache.org>]

gsmiller commented on a change in pull request #133:
URL: https://github.com/apache/lucene/pull/133#discussion_r632717530



##########
File path: lucene/facet/src/java/org/apache/lucene/facet/StringValueFacetCounts.java
##########
@@ -0,0 +1,371 @@
+/*
+ * 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.facet;
+
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import org.apache.lucene.index.DocValues;
+import org.apache.lucene.index.IndexReader;
+import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.index.MultiDocValues;
+import org.apache.lucene.index.OrdinalMap;
+import org.apache.lucene.index.ReaderUtil;
+import org.apache.lucene.index.SortedSetDocValues;
+import org.apache.lucene.search.ConjunctionDISI;
+import org.apache.lucene.search.DocIdSetIterator;
+import org.apache.lucene.search.MatchAllDocsQuery;
+import org.apache.lucene.util.BytesRef;
+import org.apache.lucene.util.LongValues;
+
+/**
+ * Compute facet counts from a previously indexed {@link SortedSetDocValues} or {@link
+ * org.apache.lucene.index.SortedDocValues} field. This approach will execute facet counting against
+ * the string values found in the specified field, with no assumptions on their format. Unlike
+ * {@link org.apache.lucene.facet.sortedset.SortedSetDocValuesFacetCounts}, no assumption is made
+ * about a "dimension" path component being indexed. Because of this, the field itself is
+ * effectively treated as the "dimension", and counts for all unique string values are produced.
+ * This approach is meant to compliment {@link LongValueFacetCounts} in that they both provide facet
+ * counting on a doc value field with no assumptions of content.
+ *
+ * <p>This implementation is useful if you want to dynamically count against any string doc value
+ * field without relying on {@link FacetField} and {@link FacetsConfig}. The disadvantage is that a
+ * separate field is required for each "dimension". If you want to pack multiple dimensions into the
+ * same doc values field, you probably want one of {@link
+ * org.apache.lucene.facet.taxonomy.FastTaxonomyFacetCounts} or {@link
+ * org.apache.lucene.facet.sortedset.SortedSetDocValuesFacetCounts}.
+ *
+ * <p>Note that there is an added cost on every {@link IndexReader} open to create a new {@link
+ * StringDocValuesReaderState}. Also note that this class should be instantiated and used from a
+ * single thread, because it holds a thread-private instance of {@link SortedSetDocValues}.
+ *
+ * @lucene.experimental
+ */
+// TODO: Add a concurrent version much like ConcurrentSortedSetDocValuesFacetCounts?
+public class StringValueFacetCounts extends Facets {
+
+  private final IndexReader reader;
+  private final String field;
+  private final OrdinalMap ordinalMap;
+  private final SortedSetDocValues docValues;
+
+  private final int[] counts;
+
+  private int totalDocCount = 0;

Review comment:
       Good point; will remove.




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