Github user jkbradley commented on a diff in the pull request: https://github.com/apache/spark/pull/3643#discussion_r21863325 --- Diff: mllib/src/main/scala/org/apache/spark/mllib/util/MLUtils.scala --- @@ -264,6 +263,92 @@ object MLUtils { } Vectors.fromBreeze(vector1) } + + /** + * Returns the squared distance between two Vectors. + */ + private[util] def vectorSquaredDistance(v1: Vector, v2: Vector): Double = { + var squaredDistance = 0.0 + (v1, v2) match { + case (v1: SparseVector, v2: SparseVector) => + val v1Values = v1.values + val v1Indices = v1.indices + val v2Values = v2.values + val v2Indices = v2.indices + val nnzv1 = v1Indices.size + val nnzv2 = v2Indices.size + + var kv1 = 0 + var kv2 = 0 + var score = 0.0 + while (kv1 < nnzv1) { + val iv1 = v1Indices(kv1) + + if (kv2 >= nnzv2 || iv1 < v2Indices(kv2)) { + score = v1Values(kv1) + squaredDistance += score * score + } + while (kv2 < nnzv2 && v2Indices(kv2) < iv1) { + score = v2Values(kv2) + squaredDistance += score * score + kv2 += 1 + } + if (kv2 < nnzv2 && v2Indices(kv2) == iv1) { + score = v1Values(kv1) - v2Values(kv2) + squaredDistance += score * score + kv2 += 1 + } + kv1 += 1 + } + + case (v1: SparseVector, v2: DenseVector) if v1.indices.length / v1.size < 0.5 => + squaredDistance = vectorSquaredDistance(v1, v2) + + case (v1: DenseVector, v2: SparseVector) if v2.indices.length / v2.size < 0.5 => + squaredDistance = vectorSquaredDistance(v2, v1) + + case (v1, v2) => + squaredDistance = v1.toArray.zip(v2.toArray).foldLeft(0.0)((distance, elems) => { --- End diff -- scala style: Use "{" for multiline foldLeft argument. No need to enclose right-hand side of "=>" with braces "{}". ``` squaredDistance = v1.toArray.zip(v2.toArray).foldLeft(0.0){ (distance, elems) => val score = elems._1 - elems._2 distance + score * score } ```
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