Github user mengxr commented on a diff in the pull request: https://github.com/apache/spark/pull/3435#discussion_r20847175 --- Diff: mllib/src/main/scala/org/apache/spark/mllib/feature/StandardScaler.scala --- @@ -97,30 +97,57 @@ class StandardScalerModel private[mllib] ( override def transform(vector: Vector): Vector = { require(mean.size == vector.size) if (withMean) { - vector.toBreeze match { - case dv: BDV[Double] => - val output = vector.toBreeze.copy - var i = 0 - while (i < output.length) { - output(i) = (output(i) - mean(i)) * (if (withStd) factor(i) else 1.0) - i += 1 + // By default, Scala generates Java methods for member variables. So every time when + // the member variables are accessed, `invokespecial` will be called which is expensive. + // This can be avoid by having a local reference of `shift`. + val localShift = shift --- End diff -- `shift` is only used in this branch. Shall we just put `val shift = mean.toArray` here instead of having a member variable?
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