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From: tillrohrmann <git@git.apache.org>
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Subject: [GitHub] flink pull request: [FLINK-1745] Add exact
 k-nearest-neighbours al...
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Message-Id: <20151008092056.95A22E054B@git1-us-west.apache.org>
Date: Thu,  8 Oct 2015 09:20:56 +0000 (UTC)

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

    https://github.com/apache/flink/pull/1220#discussion_r41492452
  
    --- Diff: flink-staging/flink-ml/src/main/scala/org/apache/flink/ml/nn/QuadTree.scala ---
    @@ -0,0 +1,305 @@
    +
    +/*
    + * 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.flink.ml.nn.util
    +
    +import org.apache.flink.ml.math.Vector
    +import org.apache.flink.ml.metrics.distances.DistanceMetric
    +
    +import scala.collection.mutable.ListBuffer
    +import scala.collection.mutable.PriorityQueue
    +
    +/**
    + * n-dimensional QuadTree data structure; partitions
    + * spatial data for faster queries (e.g. KNN query)
    + * The skeleton of the data structure was initially
    + * based off of the 2D Quadtree found here:
    + * http://www.cs.trinity.edu/~mlewis/CSCI1321-F11/Code/src/util/Quadtree.scala
    + *
    + * Many additional methods were added to the class both for
    + * efficient KNN queries and generalizing to n-dim.
    + *
    + * @param minVec
    + * @param maxVec
    + */
    +class QuadTree(minVec:ListBuffer[Double], maxVec:ListBuffer[Double],distMetric:DistanceMetric){
    +  var maxPerBox = 20
    +
    +  class Node(c:ListBuffer[Double],L:ListBuffer[Double], var children:ListBuffer[Node]) {
    +
    +    var objects = new ListBuffer[Vector]
    +
    +    /** for testing purposes only; used in QuadTreeSuite.scala
    +      *
    +      * @return
    +      */
    +    def getCenterLength(): (ListBuffer[Double], ListBuffer[Double]) = {
    +      (c, L)
    +    }
    +
    +    def contains(obj: Vector): Boolean = {
    +      overlap(obj, 0.0)
    +    }
    +
    +    /** Tests if obj is within a radius of the node
    +      *
    +      * @param obj
    +      * @param radius
    +      * @return
    +      */
    +    def overlap(obj: Vector, radius: Double): Boolean = {
    +      var count = 0
    +      for (i <- 0 to obj.size - 1) {
    +        if (obj(i) - radius < c(i) + L(i) / 2 && obj(i) + radius > c(i) - L(i) / 2) {
    +          count += 1
    +        }
    +      }
    +
    +      if (count == obj.size) {
    +        return true
    +      } else {
    +        return false
    +      }
    +    }
    +
    +    /** Tests if obj is near a node:  minDist is defined so that every point in the box
    +      * has distance to obj greater than minDist
    +      * (minDist adopted from "Nearest Neighbors Queries" by N. Roussopoulos et al.)
    +      *
    +      * @param obj
    +      * @param radius
    +      * @return
    +      */
    +    def isNear(obj: Vector, radius: Double): Boolean = {
    +      if (minDist(obj) < radius) {
    +        true
    +      } else {
    +        false
    +      }
    +    }
    +
    +    def minDist(obj: Vector): Double = {
    +      var minDist = 0.0
    +      for (i <- 0 to obj.size - 1) {
    +        if (obj(i) < c(i) - L(i) / 2) {
    +          minDist += math.pow(obj(i) - c(i) + L(i) / 2, 2)
    +        } else if (obj(i) > c(i) + L(i) / 2) {
    +          minDist += math.pow(obj(i) - c(i) - L(i) / 2, 2)
    +        }
    +      }
    +      return minDist
    +    }
    +
    +    def whichChild(obj:Vector):Int = {
    +
    +      var count = 0
    +      for (i <- 0 to obj.size - 1){
    +        if (obj(i) > c(i)) {
    +          count += Math.pow(2,i).toInt
    +        }
    +      }
    +      count
    +    }
    +
    +    def makeChildren() {
    +      var cBuff = new ListBuffer[ListBuffer[Double]]
    +      cBuff += c
    +      var Childrennodes = new ListBuffer[Node]
    +      val cPart = partitionBox(cBuff,L,L.length)
    +      for (i <- cPart.indices){
    +        Childrennodes = Childrennodes :+ new Node(cPart(i), L.map(x => x/2.0), null)
    +
    +      }
    +      children = Childrennodes.clone()
    +    }
    +
    +    /**
    +      * Recursive function that partitions a n-dim box by taking the (n-1) dimensional
    +      * plane through the center of the box keeping the n-th coordinate fixed,
    +      *  then shifting it in the n-th direction up and down
    +      * and recursively applying partitionBox to the two shifted (n-1) dimensional planes.
    +     *
    +     * @param cPart
    +     * @param L
    +     * @param dim
    +     * @return
    +     */
    +    def partitionBox(cPart:ListBuffer[ListBuffer[Double]],L:ListBuffer[Double], dim:Int):
    +    ListBuffer[ListBuffer[Double]]=
    +    {
    +      if (L.length == 1){
    +
    +        var cPartDown = cPart.clone()
    +        //// shift center up and down
    +        val cPartUp = cPart.map{v => v.patch(dim-1, Seq(v(dim - 1) + L(dim-1)/4), 1)}
    +        cPartDown = cPartDown.map{v => v.patch(dim-1, Seq(v(dim - 1) - L(dim-1)/4), 1)}
    +
    +        return cPartDown ++ cPartUp
    --- End diff --
    
    returns are not very scalaesque. Why not putting the following code in an `else` branch?


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