Github user jihoonson commented on a diff in the pull request:
https://github.com/apache/tajo/pull/200#discussion_r18822124
--- Diff:
tajo-catalog/tajo-catalog-common/src/main/java/org/apache/tajo/catalog/statistics/EquiWidthHistogram.java
---
@@ -0,0 +1,92 @@
+/**
+ * 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.tajo.catalog.statistics;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.apache.tajo.catalog.proto.CatalogProtos.HistogramProto;
+import org.apache.tajo.util.TUtil;
+
+public class EquiWidthHistogram extends Histogram {
+
+ public EquiWidthHistogram() {
+ super();
+ }
+
+ public EquiWidthHistogram(HistogramProto proto) {
+ super(proto);
+ }
+
+ @Override
+ public boolean construct(List<Double> samples) {
+ int numBuckets = samples.size() > DEFAULT_MAX_BUCKETS ?
DEFAULT_MAX_BUCKETS : samples.size();
+ return construct(samples, numBuckets);
+ }
+
+ /**
+ * Originally, an EquiWidth histogram is constructed by dividing the
entire value range of the data points into
+ * buckets of equal sizes. Here, we construct it similarly, then improve
it by removing empty buckets, to save disk
+ * space and processing time, and by compacting the buckets' boundaries,
to increase selectivity estimation accuracy.
+ *
+ * Note that, this function, which allows the specification of the
(maximum) number of buckets, should be called
+ * directly only in the unit tests. In non-test cases, the
construct(samples) version above should be used.
+ */
+ public boolean construct(List<Double> samples, int numBuckets) {
+ isReady = false;
+ buckets = TUtil.newList();
+ Double globalMin = Double.MAX_VALUE;
+ Double globalMax = -Double.MAX_VALUE;
+ List<Double> bMinValues = new ArrayList<Double>(numBuckets);
+ List<Double> bMaxValues = new ArrayList<Double>(numBuckets);
+ List<Long> bFrequencies = new ArrayList<Long>(numBuckets);
+
+ for (Double p : samples) {
+ if (p < globalMin) globalMin = p;
+ if (p > globalMax) globalMax = p;
+ }
+ double bWidth = (globalMax - globalMin) / numBuckets;
+
+ for (int i = 0; i < numBuckets; i++) {
+ bMinValues.add(Double.MAX_VALUE);
+ bMaxValues.add(-Double.MAX_VALUE);
+ bFrequencies.add(0l);
+ }
+
+ for (Double p : samples) {
+ int bIndex = (int) Math.round(Math.floor((p - globalMin) / bWidth));
--- End diff --
Do you have any reasons for conducting the round after floor?
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