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From: mengxr <git@git.apache.org>
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Subject: [GitHub] spark pull request: [WIP] [SPARK-1328] Add vector statistics
Content-Type: text/plain
Message-Id: <20140403050309.2459E939424@tyr.zones.apache.org>
Date: Thu,  3 Apr 2014 05:03:09 +0000 (UTC)

Github user mengxr commented on a diff in the pull request:

    https://github.com/apache/spark/pull/268#discussion_r11239093
  
    --- Diff: mllib/src/main/scala/org/apache/spark/mllib/rdd/VectorRDDFunctions.scala ---
    @@ -0,0 +1,179 @@
    +/*
    + * 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.mllib.rdd
    +
    +import breeze.linalg.{axpy, Vector => BV}
    +
    +import org.apache.spark.mllib.linalg.{Vectors, Vector}
    +import org.apache.spark.rdd.RDD
    +
    +/**
    + * Trait of the summary statistics, including mean, variance, count, max, min, and non-zero elements
    + * count.
    + */
    +trait VectorRDDStatisticalSummary {
    +  def mean: Vector
    +  def variance: Vector
    +  def totalCount: Long
    +  def numNonZeros: Vector
    +  def max: Vector
    +  def min: Vector
    +}
    +
    +/**
    + * Aggregates [[org.apache.spark.mllib.rdd.VectorRDDStatisticalSummary VectorRDDStatisticalSummary]]
    + * together with add() and merge() function.
    + */
    +private class Aggregator(
    +    val currMean: BV[Double],
    +    val currM2n: BV[Double],
    +    var totalCnt: Double,
    +    val nnz: BV[Double],
    +    val currMax: BV[Double],
    +    val currMin: BV[Double]) extends VectorRDDStatisticalSummary with Serializable {
    +
    +  // lazy val is used for computing only once time. Same below.
    +  override lazy val mean = Vectors.fromBreeze(currMean :* nnz :/ totalCnt)
    --- End diff --
    
    If the user call this method twice, just generate the vectors twice. We need to keep a small footprint within the aggregator.


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