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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.spark.ml.recommendation
import scala.language.implicitConversions
import scala.reflect.runtime.universe.TypeTag
import org.apache.spark.sql.{Encoder, Encoders}
import org.apache.spark.sql.catalyst.encoders.ExpressionEncoder
import org.apache.spark.sql.expressions.Aggregator
import org.apache.spark.util.BoundedPriorityQueue
/**
* Works on rows of the form (K1, K2, V) where K1 & K2 are IDs and V is the score value. Finds
* the top `num` K2 items based on the given Ordering.
*/
private[recommendation] class TopByKeyAggregator[K1: TypeTag, K2: TypeTag, V: TypeTag]
(num: Int, ord: Ordering[(K2, V)])
extends Aggregator[(K1, K2, V), BoundedPriorityQueue[(K2, V)], Array[(K2, V)]] {
override def zero: BoundedPriorityQueue[(K2, V)] = new BoundedPriorityQueue[(K2, V)](num)(ord)
override def reduce(
q: BoundedPriorityQueue[(K2, V)],
a: (K1, K2, V)): BoundedPriorityQueue[(K2, V)] = {
q += {(a._2, a._3)}
}
override def merge(
q1: BoundedPriorityQueue[(K2, V)],
q2: BoundedPriorityQueue[(K2, V)]): BoundedPriorityQueue[(K2, V)] = {
q1 ++= q2
}
override def finish(r: BoundedPriorityQueue[(K2, V)]): Array[(K2, V)] = {
r.toArray.sorted(ord.reverse)
}
override def bufferEncoder: Encoder[BoundedPriorityQueue[(K2, V)]] = {
Encoders.kryo[BoundedPriorityQueue[(K2, V)]]
}
override def outputEncoder: Encoder[Array[(K2, V)]] = ExpressionEncoder[Array[(K2, V)]]()
}
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