Attributes with Many Values

Problem:

• If attribute has many values, Gain will select it
• Imagine using $Date = Jun\_3\_1996$ as attribute

One approach: use GainRatio instead

$$GainRatio(S,A) \equiv \frac{Gain(S,A)}{SplitInformation(S,A)}$$

$$SplitInformation(S,A) \equiv - \sum_{i=1}^{c} \frac{\vert S_{... ...}{\vert S\vert} \log_{2} \frac{\vert S_{i}\vert}{\vert S\vert}$$

where S_i is subset of S for which A has value v_i