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From: chiwanpark <git@git.apache.org>
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References: <git-pr-861-flink@git.apache.org>
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Subject: [GitHub] flink pull request: [Flink-2030][ml]Data Set Statistics and
 Histog...
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Message-Id: <20150815174723.6EAE9DFFD5@git1-us-west.apache.org>
Date: Sat, 15 Aug 2015 17:47:23 +0000 (UTC)

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

    https://github.com/apache/flink/pull/861#discussion_r37137658
  
    --- Diff: flink-staging/flink-ml/src/main/scala/org/apache/flink/ml/statistics/CategoricalHistogram.scala ---
    @@ -0,0 +1,135 @@
    +/*
    + * 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.statistics
    +
    +import scala.collection.mutable
    +
    +/** Implementation of a discrete valued online histogram
    +  *
    +  * =Parameters=
    +  * -[[numCategories]]:
    +  *   Number of categories in the histogram
    +  */
    +case class CategoricalHistogram(numCategories: Int) extends OnlineHistogram {
    +
    +  require(numCategories > 0, "Capacity must be greater than zero")
    +  val data = new mutable.HashMap[Double, Int]()
    +
    +  /** Number of categories in the histogram
    +    *
    +    * @return number of categories
    +    */
    +  override def bins: Int = {
    +    numCategories
    +  }
    +
    +  /** Increment count of category c
    +    *
    +    * @param c category whose count needs to be incremented
    +    */
    +  override def add(c: Double): Unit = {
    +    if (data.get(c).isEmpty) {
    +      require(data.size < numCategories, "Insufficient capacity. Failed to add.")
    +      data.put(c, 1)
    +    } else {
    +      data.update(c, data.get(c).get + 1)
    +    }
    +  }
    +
    +  /** Merges the histogram with h and returns a new histogram
    +    *
    +    * @param h histogram to be merged
    +    * @param B number of categories in the resultant histogram.
    +    *          (Default: ```0```, number of categories will be the size of union of categories in
    +    *          both histograms)
    +    * @return Merged histogram with capacity B
    +    */
    +  override def merge(h: OnlineHistogram, B: Int = 0): CategoricalHistogram = {
    +    h match {
    +      case h1: CategoricalHistogram => {
    +        val finalMap = new mutable.HashMap[Double, Int]()
    +        data.iterator.foreach(x => finalMap.put(x._1, x._2))
    +        h1.data.iterator.foreach(x => {
    +          if (finalMap.get(x._1).isEmpty) {
    +            finalMap.put(x._1, x._2)
    +          } else {
    +            finalMap.update(x._1, x._2 + finalMap.get(x._1).get)
    +          }
    +        })
    +        require(B == 0 || finalMap.size <= B, "Insufficient capacity. Failed to merge")
    +        val countBuffer = new mutable.ArrayBuffer[(Double, Int)]()
    +        finalMap.iterator.foreach(x => countBuffer += ((x._1, x._2)))
    +        var finalSize = finalMap.size
    +        if (B > 0) {
    +          finalSize = B
    +        }
    +        val ret = new CategoricalHistogram(finalSize)
    +        ret.loadData(countBuffer.toArray)
    +        ret
    +      }
    +      case default =>
    +        throw new RuntimeException("Only a categorical histogram is allowed to be merged with a " +
    +          "categorical histogram")
    +    }
    +  }
    +
    +  /** Number of elements in category c
    +    *
    +    * @return Number of points in category c
    +    */
    +  def count(c: Double): Int = {
    +    if (data.get(c).isEmpty) {
    +      return 0
    +    }
    +    data.get(c).get
    +  }
    +
    +  /** Returns the total number of elements in the histogram
    +    *
    +    * @return total number of elements added so far
    +    */
    +  override def total: Int = {
    +    var result = 0
    +    data.valuesIterator.foreach(x => result += x)
    +    result
    +  }
    --- End diff --
    
    We can implement `total` method without mutable variable.
    
    ```scala
    override def total: Int = data.valuesIterator.sum
    ```


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