1 | /*************************************************************************/ |
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2 | /* */ |
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3 | /* Calculate information, information gain, and print dists */ |
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4 | /* -------------------------------------------------------- */ |
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5 | /* */ |
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6 | /*************************************************************************/ |
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7 | |
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8 | #include "buildex.i" |
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9 | |
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10 | |
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11 | /*************************************************************************/ |
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12 | /* */ |
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13 | /* Determine the worth of a particular split according to the */ |
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14 | /* operative criterion */ |
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15 | /* */ |
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16 | /* Parameters: */ |
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17 | /* SplitInfo: potential info of the split */ |
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18 | /* SplitGain: gain in info of the split */ |
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19 | /* MinGain: gain above which the Gain Ratio */ |
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20 | /* may be used */ |
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21 | /* */ |
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22 | /* If the Gain criterion is being used, the information gain of */ |
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23 | /* the split is returned, but if the Gain Ratio criterion is */ |
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24 | /* being used, the ratio of the information gain of the split to */ |
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25 | /* its potential information is returned. */ |
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26 | /* */ |
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27 | /*************************************************************************/ |
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28 | |
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29 | float Worth(ThisInfo, ThisGain, MinGain) |
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30 | /* ----- */ |
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31 | float ThisInfo, ThisGain, MinGain; { |
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32 | if (GAINRATIO) { |
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33 | if (ThisGain >= MinGain - Epsilon && ThisInfo > Epsilon) { |
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34 | return ThisGain / ThisInfo; |
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35 | } else { |
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36 | return -Epsilon; |
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37 | } |
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38 | } else { |
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39 | return (ThisInfo > 0 && ThisGain > -Epsilon ? ThisGain : -Epsilon); |
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40 | } |
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41 | } |
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42 | |
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43 | /*************************************************************************/ |
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44 | /* */ |
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45 | /* Zero the frequency tables Freq[][] and ValFreq[] up to MaxVal */ |
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46 | /* */ |
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47 | /*************************************************************************/ |
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48 | |
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49 | ResetFreq(MaxVal, Freq, ValFreq) |
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50 | /* --------- */ |
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51 | DiscrValue MaxVal; ItemCount** Freq; ItemCount* ValFreq; { |
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52 | DiscrValue v; |
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53 | ClassNo c; |
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54 | |
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55 | #pragma omp parallel for private(v) |
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56 | ForEach(v, 0, MaxVal) { |
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57 | ForEach(c, 0, MaxClass) { |
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58 | Freq[v][c] = 0; |
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59 | } |
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60 | ValFreq[v] = 0; |
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61 | } |
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62 | } |
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63 | |
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64 | /*************************************************************************/ |
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65 | /* */ |
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66 | /* Given tables Freq[][] and ValFreq[], compute the information gain. */ |
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67 | /* */ |
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68 | /* Parameters: */ |
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69 | /* BaseInfo: average information for all items with */ |
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70 | /* known values of the test attribute */ |
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71 | /* UnknownRate: fraction of items with unknown ditto */ |
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72 | /* MaxVal: number of forks */ |
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73 | /* TotalItems: number of items with known values of */ |
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74 | /* test att */ |
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75 | /* */ |
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76 | /* where Freq[x][y] contains the no. of cases with value x for a */ |
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77 | /* particular attribute that are members of class y, */ |
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78 | /* and ValFreq[x] contains the no. of cases with value x for a */ |
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79 | /* particular attribute */ |
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80 | /* */ |
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81 | /*************************************************************************/ |
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82 | |
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83 | float ComputeGain(BaseInfo, UnknFrac, MaxVal, TotalItems) |
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84 | /* ----------- */ |
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85 | float BaseInfo, UnknFrac;DiscrValue MaxVal;ItemCount TotalItems; { |
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86 | DiscrValue v; |
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87 | float ThisInfo = 0.0, ThisGain, TotalInfo(); |
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88 | short ReasonableSubsets = 0; |
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89 | |
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90 | /* Check whether all values are unknown or the same */ |
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91 | |
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92 | if (!TotalItems) |
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93 | return -Epsilon; |
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94 | |
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95 | /* There must be at least two subsets with MINOBJS items */ |
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96 | |
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97 | ForEach(v, 1, MaxVal) { |
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98 | if (ValFreq[v] >= MINOBJS) |
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99 | ReasonableSubsets++; |
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100 | } |
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101 | if (ReasonableSubsets < 2) |
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102 | return -Epsilon; |
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103 | |
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104 | /* Compute total info after split, by summing the |
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105 | info of each of the subsets formed by the test */ |
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106 | |
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107 | //#pragma omp parallel for reduction(+:ThisInfo) |
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108 | ForEach(v, 1, MaxVal) { |
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109 | ThisInfo += TotalInfo(Freq[v], 0, MaxClass); |
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110 | } |
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111 | |
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112 | /* Set the gain in information for all items, adjusted for unknowns */ |
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113 | |
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114 | ThisGain = (1 - UnknFrac) * (BaseInfo - ThisInfo / TotalItems); |
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115 | |
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116 | Verbosity(5) |
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117 | printf( |
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118 | "ComputeThisGain: items %.1f info %.3f base %.3f unkn %.3f result %.3f\n", |
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119 | TotalItems + ValFreq[0], ThisInfo, BaseInfo, UnknFrac, ThisGain); |
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120 | |
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121 | return ThisGain; |
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122 | } |
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123 | |
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124 | float ComputeGain_Discr(BaseInfo, UnknFrac, MaxVal, TotalItems, Freq, ValFreq) |
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125 | /* ----------- */ |
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126 | float BaseInfo, UnknFrac;DiscrValue MaxVal;ItemCount TotalItems; ItemCount** Freq; ItemCount* ValFreq; { |
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127 | DiscrValue v; |
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128 | float ThisInfo = 0.0, ThisGain, TotalInfo(); |
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129 | short ReasonableSubsets = 0; |
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130 | |
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131 | /* Check whether all values are unknown or the same */ |
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132 | |
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133 | if (!TotalItems) |
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134 | return -Epsilon; |
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135 | |
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136 | /* There must be at least two subsets with MINOBJS items */ |
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137 | |
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138 | ForEach(v, 1, MaxVal) { |
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139 | if (ValFreq[v] >= MINOBJS) |
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140 | ReasonableSubsets++; |
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141 | } |
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142 | if (ReasonableSubsets < 2) |
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143 | return -Epsilon; |
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144 | |
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145 | /* Compute total info after split, by summing the |
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146 | info of each of the subsets formed by the test */ |
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147 | |
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148 | ForEach(v, 1, MaxVal) { |
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149 | ThisInfo += TotalInfo(Freq[v], 0, MaxClass); |
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150 | } |
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151 | |
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152 | /* Set the gain in information for all items, adjusted for unknowns */ |
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153 | |
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154 | ThisGain = (1 - UnknFrac) * (BaseInfo - ThisInfo / TotalItems); |
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155 | |
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156 | Verbosity(5) |
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157 | printf( |
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158 | "ComputeThisGain: items %.1f info %.3f base %.3f unkn %.3f result %.3f\n", |
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159 | TotalItems + ValFreq[0], ThisInfo, BaseInfo, UnknFrac, ThisGain); |
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160 | |
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161 | return ThisGain; |
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162 | } |
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163 | |
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164 | /*************************************************************************/ |
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165 | /* */ |
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166 | /* Compute the total information in V[ MinVal..MaxVal ] */ |
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167 | /* */ |
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168 | /*************************************************************************/ |
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169 | |
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170 | float TotalInfo(V, MinVal, MaxVal) |
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171 | /* --------- */ |
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172 | ItemCount V[];DiscrValue MinVal, MaxVal; { |
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173 | DiscrValue v; |
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174 | float Sum = 0.0; |
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175 | ItemCount N, TotalItems = 0; |
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176 | |
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177 | ForEach(v, MinVal, MaxVal) { |
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178 | N = V[v]; |
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179 | |
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180 | Sum += N * Log(N); |
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181 | TotalItems += N; |
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182 | } |
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183 | |
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184 | return TotalItems * Log(TotalItems) - Sum; |
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185 | } |
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186 | |
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187 | /*************************************************************************/ |
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188 | /* */ |
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189 | /* Print distribution table for given attribute */ |
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190 | /* */ |
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191 | /*************************************************************************/ |
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192 | |
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193 | PrintDistribution(Att, MaxVal, ShowNames) |
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194 | /* ----------------- */ |
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195 | Attribute Att;DiscrValue MaxVal;Boolean ShowNames; { |
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196 | DiscrValue v; |
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197 | ClassNo c; |
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198 | String Val; |
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199 | |
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200 | printf("\n\t\t\t "); |
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201 | ForEach(c, 0, MaxClass) { |
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202 | printf("%7.6s", ClassName[c]); |
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203 | } |
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204 | printf("\n"); |
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205 | |
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206 | ForEach(v, 0, MaxVal) { |
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207 | if (ShowNames) { |
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208 | Val = (!v ? "unknown" : MaxAttVal[Att] ? AttValName[Att][v] : v |
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209 | == 1 ? "below" : "above"); |
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210 | printf("\t\t[%-7.7s:", Val); |
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211 | } else { |
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212 | printf("\t\t[%-7d:", v); |
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213 | } |
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214 | |
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215 | ForEach(c, 0, MaxClass) { |
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216 | printf(" %6.1f", Freq[v][c]); |
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217 | } |
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218 | |
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219 | printf("]\n"); |
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220 | } |
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221 | } |
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222 | |
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223 | PrintDistribution_Discr(Att, MaxVal, ShowNames, Freq) |
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224 | /* ----------------- */ |
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225 | Attribute Att;DiscrValue MaxVal;Boolean ShowNames; ItemCount** Freq;{ |
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226 | DiscrValue v; |
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227 | ClassNo c; |
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228 | String Val; |
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229 | |
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230 | printf("\n\t\t\t "); |
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231 | ForEach(c, 0, MaxClass) { |
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232 | printf("%7.6s", ClassName[c]); |
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233 | } |
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234 | printf("\n"); |
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235 | |
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236 | ForEach(v, 0, MaxVal) { |
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237 | if (ShowNames) { |
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238 | Val = (!v ? "unknown" : MaxAttVal[Att] ? AttValName[Att][v] : v |
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239 | == 1 ? "below" : "above"); |
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240 | printf("\t\t[%-7.7s:", Val); |
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241 | } else { |
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242 | printf("\t\t[%-7d:", v); |
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243 | } |
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244 | |
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245 | ForEach(c, 0, MaxClass) { |
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246 | printf(" %6.1f", Freq[v][c]); |
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247 | } |
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248 | |
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249 | printf("]\n"); |
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250 | } |
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251 | } |
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