wayang-commons/wayang-basic/src/main/java/org/apache/wayang/basic/operators/DistinctOperator.java

/*
 * 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.wayang.basic.operators;

import java.util.Optional;
import org.apache.commons.lang3.Validate;
import org.apache.wayang.core.api.Configuration;
import org.apache.wayang.core.optimizer.cardinality.CardinalityEstimator;
import org.apache.wayang.core.optimizer.cardinality.DefaultCardinalityEstimator;
import org.apache.wayang.core.plan.wayangplan.UnaryToUnaryOperator;
import org.apache.wayang.core.types.DataSetType;


/**
 * This operator returns the distinct elements in this dataset.
 */
public class DistinctOperator<Type> extends UnaryToUnaryOperator<Type, Type> {


    /**
     * Creates a new instance.
     *
     * @param type type of the dataunit elements
     */
    public DistinctOperator(DataSetType<Type> type) {
        super(type, type, false);
    }

    /**
     * Creates a new instance.
     *
     * @param typeClass type of the dataunit elements
     */
    public DistinctOperator(Class<Type> typeClass) {
        this(DataSetType.createDefault(typeClass));
    }

    /**
     * Copies an instance (exclusive of broadcasts).
     *
     * @param that that should be copied
     */
    public DistinctOperator(DistinctOperator<Type> that) {
        super(that);
    }

    @Override
    public Optional<CardinalityEstimator> createCardinalityEstimator(
            final int outputIndex,
            final Configuration configuration) {
        Validate.inclusiveBetween(0, this.getNumOutputs() - 1, outputIndex);
        // TODO: Come up with a dynamic estimator.
        // Assume with a confidence of 0.7 that 70% of the data quanta are pairwise distinct.
        return Optional.of(new DefaultCardinalityEstimator(0.7d, 1, this.isSupportingBroadcastInputs(),
                inputCards -> (long) (inputCards[0] * 0.7d)));
    }
}