A new algorithm for combining the local and global discretization methods

Discretizing continuous attributes in an information table is a major problem in rough set theory and a NP-hard problem also. To solve it, the paper proposed a new method. The paper firstly introduced the concept of breaking points while explaining its role in this algorithm, and described the discretization essential matter. And then defined a formula for scaling the attributes importance and the breaking points importance in the rough sets boundary region respectively, and proved four theorems about them. By use of the above concepts, formulas, theorems and combining the local discretization methods and global ones, the paper put forward an algorithm for discretization problem. This algorithm discretized it on single attribute after discretizing the information table on all attributes, and meanwhile it continually combined the unimportant breaking points and remained the important ones with the iterative constraints of entropy. This algorithm was implemented in VC++ program. Illustration and experimental results indicate the algorithm is concise, effective and efficient.