io.prestosql.plugin.accumulo.iterators.MinByteArrayCombiner Maven / Gradle / Ivy

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/*
 * Licensed 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 io.prestosql.plugin.accumulo.iterators;

import com.google.common.primitives.UnsignedBytes;
import org.apache.accumulo.core.data.Key;
import org.apache.accumulo.core.data.Value;
import org.apache.accumulo.core.iterators.Combiner;

import java.util.Comparator;
import java.util.Iterator;

/**
 * A Combiner that does a lexicographic compare against values, returning the 'smallest' value
 */
public class MinByteArrayCombiner
        extends Combiner
{
    private final Comparator comparator = UnsignedBytes.lexicographicalComparator();

    @Override
    public Value reduce(Key key, Iterator iter)
    {
        Value min = null;
        while (iter.hasNext()) {
            Value test = iter.next();
            if (min == null) {
                min = new Value(test.get());
            }
            else if (comparator.compare(test.get(), min.get()) < 0) {
                min.set(test.get());
            }
        }
        return min;
    }
}