source: proiecte/Parallel-DT/R8/Src/discr.c @ 103

/*************************************************************************/
/*                                                                       */
/*      Evaluation of a test on a discrete valued attribute              */
/*      ---------------------------------------------------              */
/*                                                                       */
/*************************************************************************/

#include "buildex.i"

/*************************************************************************/
/*                                                                       */
/*  Set Info[] and Gain[] for discrete partition of items Fp to Lp       */
/*                                                                       */
/*************************************************************************/

EvalDiscreteAtt(Att, Fp, Lp, Items)
        /*  ---------------  */
        Attribute Att;ItemNo Fp, Lp;ItemCount Items; {
        ItemCount KnownItems;
        float DiscrKnownBaseInfo(), ComputeGain(), TotalInfo();

        ComputeFrequencies(Att, Fp, Lp);

        KnownItems = Items - ValFreq[0];

        /*  Special case when no known values of the attribute  */

        if (Items <= ValFreq[0]) {
                Verbosity(2)
                        printf("\tAtt %s: no known values\n", AttName[Att]);

                Gain[Att] = -Epsilon;
                Info[Att] = 0.0;
                return;
        }

        Gain[Att] = ComputeGain(DiscrKnownBaseInfo(KnownItems, MaxAttVal[Att]),
                        UnknownRate[Att], MaxAttVal[Att], KnownItems);
        Info[Att] = TotalInfo(ValFreq, 0, MaxAttVal[Att]) / Items;

        Verbosity(2) {
                printf("\tAtt %s", AttName[Att]);
                Verbosity(3)
                        PrintDistribution(Att, MaxAttVal[Att], true);
                printf("\tinf %.3f, gain %.3f\n", Info[Att], Gain[Att]);
        }

}

EvalDiscreteAtt_Discr(Att, Fp, Lp, Items, Freq_discr, ValFreq_discr, UnknownRate_discr, the_gain, the_info)
        /*  ---------------  */
        Attribute Att;ItemNo Fp, Lp;ItemCount Items; ItemCount** Freq_discr; ItemCount* ValFreq_discr; float* UnknownRate_discr;
        float* the_gain; float* the_info;{
        ItemCount KnownItems;
        float DiscrKnownBaseInfo_Discr(), ComputeGain_Discr(), TotalInfo();

        ComputeFrequencies_Discr(Att, Fp, Lp, Freq_discr, ValFreq_discr, UnknownRate_discr);

        KnownItems = Items - ValFreq_discr[0];

        /*  Special case when no known values of the attribute  */

        if (Items <= ValFreq_discr[0]) {
                Verbosity(2)
                        printf("\tAtt %s: no known values\n", AttName[Att]);

                *the_gain = -Epsilon;
                *the_info = 0.0;
                return;
        }

        *the_gain = ComputeGain_Discr(DiscrKnownBaseInfo_Discr(KnownItems, MaxAttVal[Att], Freq_discr),
                        UnknownRate_discr[Att], MaxAttVal[Att], KnownItems, Freq_discr, ValFreq_discr);
        *the_info = TotalInfo(ValFreq_discr, 0, MaxAttVal[Att]) / Items;

        Verbosity(2) {
                printf("\tAtt %s", AttName[Att]);
                Verbosity(3)
                        PrintDistribution_Discr(Att, MaxAttVal[Att], true, Freq_discr);
                printf("\tinf %.3f, gain %.3f\n", *the_info, *the_gain);
        }

}
/*************************************************************************/
/*                                                                       */
/*  Compute frequency tables Freq[][] and ValFreq[] for attribute        */
/*  Att from items Fp to Lp, and set the UnknownRate for Att             */
/*                                                                       */
/*************************************************************************/

ComputeFrequencies(Att, Fp, Lp)
        /*  ------------------  */
        Attribute Att;ItemNo Fp, Lp; {
        Description Case;
        ClassNo c;
        DiscrValue v;
        ItemCount CountItems();
        ItemNo p;

        ResetFreq(MaxAttVal[Att], Freq, ValFreq);

        /*  Determine the frequency of each class amongst cases
         with each possible value for the given attribute  */

        ForEach(p, Fp, Lp) {
                Case = Item[p];
                Freq[DVal(Case,Att)][Class(Case)] += Weight[p];
        }

        /*  Determine the frequency of each possible value for the
         given attribute  */

        ForEach(v, 0, MaxAttVal[Att]) {
                ForEach(c, 0, MaxClass) {
                        ValFreq[v] += Freq[v][c];
                }
        }

        /*  Set the rate of unknown values of the attribute  */

        UnknownRate[Att] = ValFreq[0] / CountItems(Fp, Lp);
}

ComputeFrequencies_Discr(Att, Fp, Lp, Freq_discr, ValFreq_discr, UnknownRate_discr)
        /*  ------------------  */
        Attribute Att;ItemNo Fp, Lp; ItemCount** Freq_discr; ItemCount* ValFreq_discr; float* UnknownRate_discr;{
        Description Case;
        ClassNo c;
        DiscrValue v;
        ItemCount CountItems();
        ItemNo p;

        ResetFreq_discr(MaxAttVal[Att], Freq_discr, ValFreq_discr);

        /*  Determine the frequency of each class amongst cases
         with each possible value for the given attribute  */

        ForEach(p, Fp, Lp) {
                Case = Item[p];
                Freq_discr[DVal(Case,Att)][Class(Case)] += Weight[p];
        }

        /*  Determine the frequency of each possible value for the
         given attribute  */

        ForEach(v, 0, MaxAttVal[Att]) {
                ForEach(c, 0, MaxClass) {
                        ValFreq_discr[v] += Freq_discr[v][c];
                }
        }

        /*  Set the rate of unknown values of the attribute  */

        UnknownRate_discr[Att] = ValFreq_discr[0] / CountItems(Fp, Lp);
}
/*************************************************************************/
/*                                                                       */
/*  Return the base info for items with known values of a discrete       */
/*  attribute, using the frequency table Freq[][]                        */
/*                                                                       */
/*************************************************************************/

float DiscrKnownBaseInfo(KnownItems, MaxVal)
        /*    ------------------  */
        DiscrValue MaxVal;ItemCount KnownItems; {
        ClassNo c;
        ItemCount ClassCount;
        double Sum = 0;
        DiscrValue v;

        ForEach(c, 0, MaxClass) {
                ClassCount = 0;
                ForEach(v, 1, MaxVal) {
                        ClassCount += Freq[v][c];
                }
                Sum += ClassCount * Log(ClassCount);
        }

        return (KnownItems * Log(KnownItems) - Sum) / KnownItems;
}

float DiscrKnownBaseInfo_Discr(KnownItems, MaxVal, Freq_discr)
        /*    ------------------  */
        DiscrValue MaxVal;ItemCount KnownItems; ItemCount** Freq_discr;{
        ClassNo c;
        ItemCount ClassCount;
        double Sum = 0;
        DiscrValue v;

        ForEach(c, 0, MaxClass) {
                ClassCount = 0;
                ForEach(v, 1, MaxVal) {
                        ClassCount += Freq_discr[v][c];
                }
                Sum += ClassCount * Log(ClassCount);
        }

        return (KnownItems * Log(KnownItems) - Sum) / KnownItems;
}

/*************************************************************************/
/*                                                                       */
/*  Construct and return a node for a test on a discrete attribute       */
/*                                                                       */
/*************************************************************************/

DiscreteTest(Node, Att)
        /*  ----------  */
        Tree Node;Attribute Att; {
        ItemCount CountItems();

        Sprout(Node, MaxAttVal[Att]);

        Node->NodeType = BrDiscr;
        Node->Tested = Att;
        Node->Errors = 0;
}