Package weka.core

Class MathematicalExpression

  • All Implemented Interfaces:
    RevisionHandler
    public class MathematicalExpression
extends java.lang.Object
implements RevisionHandler
    Class for evaluating a string adhering the following grammar:
     expr_list ::= expr_list expr_part | expr_part ;
 expr_part ::= expr ;
 expr      ::=   NUMBER
               | ( expr )
               | opexpr
               | varexpr
               | funcexpr
               ;
 
 opexpr    ::=   expr + expr
               | expr - expr
               | expr * expr
               | expr / expr
               ;
 
 varexpr  ::=  VARIABLE ;
 
 funcexpr ::=    abs ( expr )
               | sqrt ( expr )
               | log ( expr )
               | exp ( expr )
               | sin ( expr )
               | cos ( expr )
               | tan ( expr )
               | rint ( expr )
               | floor ( expr )
               | pow ( expr , expr )
               | ceil ( expr )
               | ifelse ( boolexpr , expr (if true) , expr (if false) )
               ;
 
 boolexpr ::=    BOOLEAN
               | true
               | false
               | expr < expr
               | expr <= expr
               | expr > expr
               | expr >= expr
               | expr = expr
               | ( boolexpr )
               | ! boolexpr
               | boolexpr & boolexpr
               | boolexpr | boolexpr
               ;
    Code example 1: 
     String expr = "pow(BASE,EXPONENT)*MULT";
 HashMap symbols = new HashMap();
 symbols.put("BASE", new Double(2));
 symbols.put("EXPONENT", new Double(9));
 symbols.put("MULT", new Double(0.1));
 double result = MathematicalExpression.evaluate(expr, symbols);
 System.out.println(expr + " and " + symbols + " = " + result);
    Code Example 2 (uses the "ifelse" construct): 
     String expr = "ifelse(I<0,pow(BASE,I*0.5),pow(BASE,I))";
 MathematicalExpression.TreeNode tree = MathematicalExpression.parse(expr);
 HashMap symbols = new HashMap();
 symbols.put("BASE", new Double(2));
 for (int i = -10; i <= 10; i++) {
   symbols.put("I", new Double(i));
   double result = MathematicalExpression.evaluate(expr, symbols);
   System.out.println(expr + " and " + symbols + " = " + result);
 }
    Version:
    $Revision: 4942 $
    Author:
    FracPete (fracpete at waikato dot ac dot nz)

    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      static double evaluate​(java.lang.String expr, java.util.HashMap symbols)
      Parses and evaluates the given expression.
      java.lang.String getRevision()
      Returns the revision string.

      • Methods inherited from class java.lang.Object

        equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Constructor Detail

      • MathematicalExpression

        public MathematicalExpression()

    • Method Detail

      • evaluate

        public static double evaluate​(java.lang.String expr,
                              java.util.HashMap symbols)
                       throws java.lang.Exception
        Parses and evaluates the given expression. Returns the result of the mathematical expression, based on the given values of the symbols.
        Parameters:
        expr - the expression to evaluate
        symbols - the symbol/value mapping
        Returns:
        the evaluated result
        Throws:
        java.lang.Exception - if something goes wrong

      • getRevision

        public java.lang.String getRevision()
        Returns the revision string.
        Specified by:
        getRevision in interface RevisionHandler
        Returns:
        the revision