Github user jkbradley commented on a diff in the pull request: https://github.com/apache/spark/pull/15148#discussion_r82445651 --- Diff: mllib/src/main/scala/org/apache/spark/ml/feature/MinHash.scala --- @@ -0,0 +1,107 @@ +/* + * 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.feature + +import scala.util.Random + +import org.apache.spark.annotation.{Experimental, Since} +import org.apache.spark.ml.linalg.{Vector, Vectors, VectorUDT} +import org.apache.spark.ml.util.Identifiable +import org.apache.spark.sql.types.StructType + +/** + * Model produced by [[MinHash]] + */ +@Experimental +@Since("2.1.0") +class MinHashModel private[ml] (override val uid: String, hashFunctions: Seq[Int => Long]) + extends LSHModel[MinHashModel] { + + @Since("2.1.0") + override protected[this] val hashFunction: Vector => Vector = { + elems: Vector => + require(elems.numNonzeros > 0, "Must have at least 1 non zero entry.") + Vectors.dense(hashFunctions.map( + func => elems.toSparse.indices.toList.map(func).min.toDouble + ).toArray) + } + + @Since("2.1.0") + override protected[ml] def keyDistance(x: Vector, y: Vector): Double = { + val xSet = x.toSparse.indices.toSet + val ySet = y.toSparse.indices.toSet + 1 - xSet.intersect(ySet).size.toDouble / xSet.union(ySet).size.toDouble + } + + @Since("2.1.0") + override protected[ml] def hashDistance(x: Vector, y: Vector): Double = { + // Since it's generated by hashing, it will be a pair of dense vectors. + x.toDense.values.zip(y.toDense.values).map(x => math.abs(x._1 - x._2)).min + } +} + +/** + * LSH class for Jaccard distance + * The input set should be represented in sparse vector form. For example, + * Vectors.sparse(10, Array[(2, 1.0), (3, 1.0), (5, 1.0)]) + * means there are 10 elements in the space. This set contains elem 2, elem 3 and elem 5 + */ +@Experimental +@Since("2.1.0") +class MinHash private[ml] (override val uid: String) extends LSH[MinHashModel] { + + private[this] val prime = 2038074743 + + @Since("2.1.0") + override def setInputCol(value: String): this.type = super.setInputCol(value) + + @Since("2.1.0") + override def setOutputCol(value: String): this.type = super.setOutputCol(value) + + @Since("2.1.0") + override def setOutputDim(value: Int): this.type = super.setOutputDim(value) + + private[this] lazy val randSeq: Seq[Int] = { + Seq.fill($(outputDim))(1 + Random.nextInt(prime - 1)).take($(outputDim)) --- End diff -- Why have ```.take(...)```?
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