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66 lines (57 loc) · 2.33 KB
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/*
* 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.arrow.algorithm.sort;
import org.apache.arrow.util.Preconditions;
import org.apache.arrow.vector.ValueVector;
/**
* Stable sorter. It compares values like ordinary comparators.
* However, when values are equal, it breaks ties by the value indices.
* Therefore, sort algorithms using this comparator always produce
* stable sort results.
* @param <V> type of the vector.
*/
public class StableVectorComparator<V extends ValueVector> extends VectorValueComparator<V> {
private final VectorValueComparator<V> innerComparator;
/**
* Constructs a stable comparator from a given comparator.
* @param innerComparator the comparator to convert to stable comparator..
*/
public StableVectorComparator(VectorValueComparator<V> innerComparator) {
this.innerComparator = innerComparator;
}
@Override
public void attachVector(V vector) {
super.attachVector(vector);
innerComparator.attachVector(vector);
}
@Override
public void attachVectors(V vector1, V vector2) {
Preconditions.checkArgument(vector1 == vector2,
"Stable comparator only supports comparing values from the same vector");
super.attachVectors(vector1, vector2);
innerComparator.attachVectors(vector1, vector2);
}
@Override
public int compareNotNull(int index1, int index2) {
int result = innerComparator.compare(index1, index2);
return result != 0 ? result : index1 - index2;
}
@Override
public VectorValueComparator<V> createNew() {
return new StableVectorComparator<V>(innerComparator.createNew());
}
}