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/*******************************************************************************
 * Copyright (c) 2015-2018 Skymind, Inc.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Apache License, Version 2.0 which is available at
 * https://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.
 *
 * SPDX-License-Identifier: Apache-2.0
 ******************************************************************************/

package org.datavec.api.transform.reduce;

import org.datavec.api.transform.ops.IAggregableReduceOp;
import org.datavec.api.transform.schema.Schema;
import org.datavec.api.writable.Writable;
import org.nd4j.shade.jackson.annotation.JsonInclude;
import org.nd4j.shade.jackson.annotation.JsonSubTypes;
import org.nd4j.shade.jackson.annotation.JsonTypeInfo;

import java.io.Serializable;
import java.util.List;

/**
 * A reducer aggregates or combines
 * a set of examples into
 * a single List
 */
@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.WRAPPER_OBJECT)
@JsonSubTypes(value = {@JsonSubTypes.Type(value = Reducer.class, name = "Reducer")})
public interface IAssociativeReducer extends Serializable {

    /**
     *
     * @param schema
     */
    void setInputSchema(Schema schema);

    /**
     *
     * @return
     */
    Schema getInputSchema();

    /**
     *
     * @param schema
     * @return
     */
    Schema transform(Schema schema);

    /**
     * An aggregation that has the property that
     * reduce(List(reduce(List(l1, l2)), l3)) = reduce(List(l1, reduce(List(l2, l3)))
     * @return
     */
    IAggregableReduceOp, List> aggregableReducer();

    /**
     *
     * @return
     */
    List getKeyColumns();

}