/* *    This program is free software; you can redistribute it and/or modify *    it under the terms of the GNU General Public License as published by *    the Free Software Foundation; either version 2 of the License, or *    (at your option) any later version. * *    This program is distributed in the hope that it will be useful, *    but WITHOUT ANY WARRANTY; without even the implied warranty of *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the *    GNU General Public License for more details. * *    You should have received a copy of the GNU General Public License *    along with this program; if not, write to the Free Software *    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. *//* *    Impurity.java *    Copyright (C) 1999 Yong Wang * */package weka.classifiers.trees.m5;import java.io.*;import java.util.*;import weka.core.*;/** * Class for handling the impurity values when spliting the instances * @author Yong Wang (yongwang@cs.waikato.ac.nz) * @version $Revision: 1.6 $ */public final class Impurity{  double n;                   // number of total instances   int attr;                   // splitting attribute   double nl;                  // number of instances in the left group   double nr;                  // number of instances in the right group   double sl;                  // sum of the left group    double sr;                  // sum of the right group   double s2l;                 // squared sum of the left group   double s2r;                 // squared sum of the right group   double sdl;                 // standard deviation of the left group   double sdr;                 // standard deviation of the right group   double vl;                  // variance of the left group   double vr;                  // variance of the right group   double sd;                  // overall standard deviation   double va;                  // overall variance   double impurity;            // impurity value;  int order;                  // order = 1, variance; order = 2, standard deviation; order = 3, the cubic root of the variance;                                // order = k, the k-th order root of the variance  /**   * Constructs an Impurity object containing the impurity values of partitioning the instances using an attribute   * @param partition the index of the last instance in the left subset   * @param attribute the attribute used in partitioning   * @param inst instances   * @param k the order of the impurity; =1, the variance; =2, the stardard deviation; =k, the k-th order root of the variance   */  public Impurity(int partition,int attribute,Instances inst,int k){    Values values = new Values(0,inst.numInstances()-1,inst.classIndex(),inst);    attr = attribute;    n   = inst.numInstances();    sd  = values.sd;     va  = values.va;    values = new Values(0,partition,inst.classIndex(),inst);    nl  = partition + 1;    sl  = values.sum;    s2l = values.sqrSum;    values = new Values(partition+1,inst.numInstances()-1,inst.classIndex(),inst);    nr  = inst.numInstances() - partition -1;    sr  = values.sum;    s2r = values.sqrSum;    order = k;    this.incremental(0,0);  }  /**   * Converts an Impurity object to a string   * @return the converted string   */  public final String  toString() {        StringBuffer text = new StringBuffer();        text.append("Print impurity values:\n");    text.append("    Number of total instances:\t" + n + "\n");    text.append("    Splitting attribute:\t\t" + attr + "\n");    text.append("    Number of the instances in the left:\t" + nl + "\n");    text.append("    Number of the instances in the right:\t" + nr + "\n");    text.append("    Sum of the left:\t\t\t" + sl + "\n");    text.append("    Sum of the right:\t\t\t" + sr + "\n");    text.append("    Squared sum of the left:\t\t" + s2l + "\n");     text.append("    Squared sum of the right:\t\t" + s2r + "\n");    text.append("    Standard deviation of the left:\t" + sdl + "\n");    text.append("    Standard deviation of the right:\t" + sdr + "\n");    text.append("    Variance of the left:\t\t" + vr + "\n");    text.append("    Variance of the right:\t\t" + vr + "\n");    text.append("    Overall standard deviation:\t\t" + sd + "\n");    text.append("    Overall variance:\t\t\t" + va + "\n");    text.append("    Impurity (order " + order + "):\t\t" + impurity + "\n");    return text.toString();  }    /**   * Incrementally computes the impurirty values   * @param value the incremental value    * @param type if type=1, value will be added to the left subset; type=-1, to the right subset; type=0, initializes   */  public final void  incremental(double value,int type){    double y=0.,yl=0.,yr=0.;    switch(type){    case 1:      nl += 1;      nr -= 1;      sl += value;      sr -= value;      s2l += value*value;      s2r -= value*value;      break;    case -1:      nl -= 1;      nr += 1;      sl -= value;      sr += value;      s2l -= value*value;      s2r += value*value;      break;    case 0:      break;    default: System.err.println("wrong type in Impurity.incremental().");    }    if(nl<=0.0){      vl=0.0;      sdl=0.0;    }    else {      vl = (nl*s2l-sl*sl)/((double)nl*((double)nl));      vl = Math.abs(vl);      sdl = Math.sqrt(vl);    }    if(nr<=0.0){      vr=0.0;      sdr=0.0;    }    else {      vr = (nr*s2r-sr*sr)/((double)nr*((double)nr));      vr = Math.abs(vr);      sdr = Math.sqrt(vr);    }    if(order <= 0)System.err.println("Impurity order less than zero in Impurity.incremental()");    else if(order == 1) {      y = va; yl = vl; yr = vr;    } else {      y  = Math.pow(va,1./order);      yl = Math.pow(vl,1./order);      yr = Math.pow(vr,1./order);    }    if(nl<=0.0 || nr<=0.0)      impurity = 0.0;    else {       impurity = y - ((double)nl/(double)n)*yl - ((double)nr/(double)n)*yr;    }  }}