analysis/org.eclipse.tracecompass.analysis.timing.core/src/org/eclipse/tracecompass/analysis/timing/core/segmentstore/statistics/SegmentStoreStatistics.java

   1 /*******************************************************************************
   2  * Copyright (c) 2015, 2016 Ericsson
   3  *
   4  * All rights reserved. This program and the accompanying materials are made
   5  * available under the terms of the Eclipse Public License v1.0 which
   6  * accompanies this distribution, and is available at
   7  * http://www.eclipse.org/legal/epl-v10.html
   8  *
   9  * Contributors:
  10  *     Bernd Hufmann - Initial API and implementation
  11  *******************************************************************************/
  12 package org.eclipse.tracecompass.analysis.timing.core.segmentstore.statistics;
  13
  14 import org.eclipse.tracecompass.segmentstore.core.BasicSegment;
  15 import org.eclipse.tracecompass.segmentstore.core.ISegment;
  16
  17 /**
  18  * Class to calculate simple segment store statistics (min, max, average)
  19  *
  20  * @author Bernd Hufmann
  21  */
  22 public class SegmentStoreStatistics {
  23     private ISegment fMin;
  24     private ISegment fMax;
  25     private long fNbSegments;
  26     private double fAverage;
  27     private double fVariance;
  28
  29     /**
  30      * Constructor
  31      */
  32     public SegmentStoreStatistics() {
  33         fMin = new BasicSegment(0, Long.MAX_VALUE);
  34         fMax = new BasicSegment(Long.MIN_VALUE, 0);
  35         fNbSegments = 0;
  36         fAverage = 0.0;
  37         fVariance = 0.0;
  38     }
  39
  40     /**
  41      * Get minimum value
  42      *
  43      * @return minimum value
  44      */
  45     public long getMin() {
  46         return fMin.getLength();
  47     }
  48
  49     /**
  50      * Get maximum value
  51      *
  52      * @return maximum value
  53      */
  54     public long getMax() {
  55         return fMax.getLength();
  56     }
  57
  58     /**
  59      * Get segment with minimum length
  60      *
  61      * @return segment with minimum length
  62      */
  63     public ISegment getMinSegment() {
  64         return fMin;
  65     }
  66
  67     /**
  68      * Get segment with maximum length
  69      *
  70      * @return segment with maximum length
  71      */
  72     public ISegment getMaxSegment() {
  73         return fMax;
  74     }
  75
  76     /**
  77      * Get number of segments analyzed
  78      *
  79      * @return number of segments analyzed
  80      */
  81     public long getNbSegments() {
  82         return fNbSegments;
  83     }
  84
  85     /**
  86      * Gets the arithmetic average
  87      *
  88      * @return arithmetic average
  89      */
  90     public double getAverage() {
  91         return fAverage;
  92     }
  93
  94     /**
  95      * Gets the standard deviation of the segments, uses the online algorithm
  96      * shown here <a href=
  97      * "https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Online_algorithm">
  98      * Wikipedia article of dec 3 2015 </a>
  99      *
 100      * @return the standard deviation of the segment store, will return NaN if
 101      *         there are less than 3 elements
 102      */
 103     public double getStdDev() {
 104         return fNbSegments > 2 ? Math.sqrt(fVariance / (fNbSegments - 1)) : Double.NaN;
 105     }
 106
 107     /**
 108      * Update the statistics based on a given segment
 109      * <p>
 110      * This is an online algorithm and must retain a complexity of O(1)
 111      *
 112      * @param segment
 113      *            the segment used for the update
 114      */
 115     public void update(ISegment segment) {
 116         long value = segment.getLength();
 117         /*
 118          * Min and max are trivial, as well as number of segments
 119          */
 120         long min = fMin.getLength();
 121         long max = fMax.getLength();
 122         fMin = min <= value ? fMin : segment;
 123         fMax = max >= value ? fMax : segment;
 124
 125         fNbSegments++;
 126         /*
 127          * The running mean is not trivial, see proof in javadoc.
 128          */
 129         double delta = value - fAverage;
 130         fAverage += delta / fNbSegments;
 131         fVariance += delta * (value - fAverage);
 132     }
 133 }