/*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
/*
* AttributeExpression.java
* Copyright (C) 2006-2012 University of Waikato, Hamilton, New Zealand
*
*/
package weka.core;
import java.io.Serializable;
import java.util.Stack;
import java.util.StringTokenizer;
import java.util.Vector;
/**
* A general purpose class for parsing mathematical expressions
* involving attribute values. Values can be provided in an array
* or in an Instance. Values are accessed in the expression by
* prefixing their index (starting at 1) with the character 'a'.
*
* <pre> Example expression: a1^2*a5/log(a7*4.0) </pre>
*
* Supported opperators: +, -, *, /, ^, log, abs, cos, exp, sqrt,
* floor, ceil, rint, tan, sin, (, ).
*
* @author Mark Hall
* @version $Revision: 8034 $
*/
public class AttributeExpression
implements Serializable, RevisionHandler {
/** for serialization */
static final long serialVersionUID = 402130123261736245L;
/**
* Interface implemented by operators and operants.
*/
private interface ExpressionComponent {};
/**
* Inner class handling an attribute index as an operand
*/
private class AttributeOperand
implements ExpressionComponent, Serializable, RevisionHandler {
/** for serialization */
static final long serialVersionUID = -7674280127286031105L;
/** the index of the attribute */
protected int m_attributeIndex;
/** true if the value of the attribute are to be multiplied by -1 */
protected boolean m_negative;
/**
* Constructor
*
* @param operand
* @param sign
* @throws Exception
*/
public AttributeOperand(String operand, boolean sign) throws Exception {
// strip the leading 'a' and set the index
m_attributeIndex = (Integer.parseInt(operand.substring(1)))-1;
m_negative = sign;
}
/**
* Return a string describing this object
* @return a string descibing the attribute operand
*/
public String toString() {
String result = "";
if (m_negative) {
result += '-';
}
return result+"a"+(m_attributeIndex+1);
}
/**
* Returns the revision string.
*
* @return the revision
*/
public String getRevision() {
return RevisionUtils.extract("$Revision: 8034 $");
}
}
/**
* Inner class for storing numeric constant opperands
*/
private class NumericOperand
implements ExpressionComponent, Serializable, RevisionHandler {
/** for serialization */
static final long serialVersionUID = 9037007836243662859L;
/** numeric constant */
protected double m_numericConst;
/**
* Constructor
*
* @param operand
* @param sign
* @throws Exception
*/
public NumericOperand(String operand, boolean sign) throws Exception {
m_numericConst = Double.valueOf(operand).doubleValue();
if (sign) {
m_numericConst *= -1.0;
}
}
/**
* Return a string describing this object
* @return a string descibing the numeric operand
*/
public String toString() {
return ""+m_numericConst;
}
/**
* Returns the revision string.
*
* @return the revision
*/
public String getRevision() {
return RevisionUtils.extract("$Revision: 8034 $");
}
}
/**
* Inner class for storing operators
*/
private class Operator
implements ExpressionComponent, Serializable, RevisionHandler {
/** for serialization */
static final long serialVersionUID = -2760353522666004638L;
/** the operator */
protected char m_operator;
/**
* Constructor
*
* @param opp the operator
*/
public Operator(char opp) {
if (!isOperator(opp)) {
throw new IllegalArgumentException("Unrecognized operator:" + opp);
}
m_operator = opp;
}
/**
* Apply this operator to the supplied arguments
* @param first the first argument
* @param second the second argument
* @return the result
*/
protected double applyOperator(double first, double second) {
switch (m_operator) {
case '+' :
return (first+second);
case '-' :
return (first-second);
case '*' :
return (first*second);
case '/' :
return (first/second);
case '^' :
return Math.pow(first,second);
}
return Double.NaN;
}
/**
* Apply this operator (function) to the supplied argument
* @param value the argument
* @return the result
*/
protected double applyFunction(double value) {
switch (m_operator) {
case 'l' :
return Math.log(value);
case 'b' :
return Math.abs(value);
case 'c' :
return Math.cos(value);
case 'e' :
return Math.exp(value);
case 's' :
return Math.sqrt(value);
case 'f' :
return Math.floor(value);
case 'h' :
return Math.ceil(value);
case 'r' :
return Math.rint(value);
case 't' :
return Math.tan(value);
case 'n' :
return Math.sin(value);
}
return Double.NaN;
}
/**
* Return a string describing this object
* @return a string descibing the operator
*/
public String toString() {
return ""+m_operator;
}
/**
* Returns the revision string.
*
* @return the revision
*/
public String getRevision() {
return RevisionUtils.extract("$Revision: 8034 $");
}
}
/** Operator stack */
private Stack<String> m_operatorStack = new Stack<String>();
/** Supported operators. l = log, b = abs, c = cos, e = exp, s = sqrt,
f = floor, h = ceil, r = rint, t = tan, n = sin */
private static final String OPERATORS = "+-*/()^lbcesfhrtn";
/** Unary functions. l = log, b = abs, c = cos, e = exp, s = sqrt,
f = floor, h = ceil, r = rint, t = tan, n = sin */
private static final String UNARY_FUNCTIONS = "lbcesfhrtn";
/** Holds the original infix expression */
private String m_originalInfix;
/** Holds the expression in postfix form */
private Vector<ExpressionComponent> m_postFixExpVector;
/** True if the next numeric constant or attribute index is negative */
private boolean m_signMod = false;
/** Holds the previous token */
private String m_previousTok = "";
/**
* Handles the processing of an infix operand to postfix
* @param tok the infix operand
* @throws Exception if there is difficulty parsing the operand
*/
private void handleOperand(String tok) throws Exception {
// if it contains an 'a' then its an attribute index
if (tok.indexOf('a') != -1) {
m_postFixExpVector.addElement(new AttributeOperand(tok,m_signMod));
} else {
try {
// should be a numeric constant
m_postFixExpVector.addElement(new NumericOperand(tok, m_signMod));
} catch (NumberFormatException ne) {
throw new Exception("Trouble parsing numeric constant");
}
}
m_signMod = false;
}
/**
* Handles the processing of an infix operator to postfix
* @param tok the infix operator
* @throws Exception if there is difficulty parsing the operator
*/
private void handleOperator(String tok) throws Exception {
boolean push = true;
char tokchar = tok.charAt(0);
if (tokchar == ')') {
String popop = " ";
do {
popop = (String)(m_operatorStack.pop());
if (popop.charAt(0) != '(') {
m_postFixExpVector.addElement(new Operator(popop.charAt(0)));
}
} while (popop.charAt(0) != '(');
} else {
int infixToc = infixPriority(tok.charAt(0));
while (!m_operatorStack.empty() &&
stackPriority(((String)(m_operatorStack.peek())).charAt(0))
>= infixToc) {
// try an catch double operators and see if the current one can
// be interpreted as the sign of an upcoming number
if (m_previousTok.length() == 1 &&
isOperator(m_previousTok.charAt(0)) &&
m_previousTok.charAt(0) != ')') {
if (tok.charAt(0) == '-') {
m_signMod = true;
} else {
m_signMod = false;
}
push = false;
break;
} else {
String popop = (String)(m_operatorStack.pop());
m_postFixExpVector.addElement(new Operator(popop.charAt(0)));
}
}
if (m_postFixExpVector.size() == 0) {
if (tok.charAt(0) == '-') {
m_signMod = true;
push = false;
}
}
if (push) {
m_operatorStack.push(tok);
}
}
}
/**
* Converts a string containing a mathematical expression in infix form
* to postfix form. The result is stored in the vector m_postfixExpVector
*
* @param infixExp the infix expression to convert
* @throws Exception if something goes wrong during the conversion
*/
public void convertInfixToPostfix(String infixExp) throws Exception {
m_originalInfix = infixExp;
infixExp = Utils.removeSubstring(infixExp, " ");
infixExp = Utils.replaceSubstring(infixExp,"log","l");
infixExp = Utils.replaceSubstring(infixExp,"abs","b");
infixExp = Utils.replaceSubstring(infixExp,"cos","c");
infixExp = Utils.replaceSubstring(infixExp,"exp","e");
infixExp = Utils.replaceSubstring(infixExp,"sqrt","s");
infixExp = Utils.replaceSubstring(infixExp,"floor","f");
infixExp = Utils.replaceSubstring(infixExp,"ceil","h");
infixExp = Utils.replaceSubstring(infixExp,"rint","r");
infixExp = Utils.replaceSubstring(infixExp,"tan","t");
infixExp = Utils.replaceSubstring(infixExp,"sin","n");
StringTokenizer tokenizer = new StringTokenizer(infixExp, OPERATORS, true);
m_postFixExpVector = new Vector<ExpressionComponent>();
while (tokenizer.hasMoreTokens()) {
String tok = tokenizer.nextToken();
if (tok.length() > 1) {
handleOperand(tok);
} else {
// probably an operator, but could be a single char operand
if (isOperator(tok.charAt(0))) {
handleOperator(tok);
} else {
// should be a numeric constant
handleOperand(tok);
}
}
m_previousTok = tok;
}
while (!m_operatorStack.empty()) {
String popop = (String)(m_operatorStack.pop());
if (popop.charAt(0) == '(' || popop.charAt(0) == ')') {
throw new Exception("Mis-matched parenthesis!");
}
m_postFixExpVector.addElement(new Operator(popop.charAt(0)));
}
}
/**
* Evaluate the expression using the supplied Instance.
* Assumes that the infix expression has been converted to
* postfix and stored in m_postFixExpVector
*
* @param instance the Instance containing values to apply
* the expression to
* @throws Exception if something goes wrong
*/
public double evaluateExpression(Instance instance)
throws Exception {
double [] vals = new double [instance.numAttributes()+1];
for(int i = 0; i < instance.numAttributes(); i++) {
if (instance.isMissing(i)) {
vals[i] = Utils.missingValue();
} else {
vals[i] = instance.value(i);
}
}
evaluateExpression(vals);
return vals[vals.length - 1];
}
/**
* Evaluate the expression using the supplied array of attribute values.
* The result is stored in the last element of the array. Assumes that
* the infix expression has been converted to postfix and stored in
* m_postFixExpVector
* @param vals the values to apply the expression to
* @throws Exception if something goes wrong
*/
public void evaluateExpression(double [] vals) throws Exception {
Stack<Double> operands = new Stack<Double>();
for (int i=0;i<m_postFixExpVector.size();i++) {
Object nextob = m_postFixExpVector.elementAt(i);
if (nextob instanceof NumericOperand) {
operands.push(new Double(((NumericOperand)nextob).m_numericConst));
} else if (nextob instanceof AttributeOperand) {
double value = vals[((AttributeOperand)nextob).m_attributeIndex];
/*if (Utils.isMissingValue(value)) {
vals[vals.length-1] = Utils.missingValue();
break;
}*/
if (((AttributeOperand)nextob).m_negative) {
value = -value;
}
operands.push(new Double(value));
} else if (nextob instanceof Operator) {
char op = ((Operator)nextob).m_operator;
if (isUnaryFunction(op)) {
double operand = ((Double)operands.pop()).doubleValue();
double result = ((Operator)nextob).applyFunction(operand);
operands.push(new Double(result));
} else {
double second = ((Double)operands.pop()).doubleValue();
double first = ((Double)operands.pop()).doubleValue();
double result = ((Operator)nextob).applyOperator(first,second);
operands.push(new Double(result));
}
} else {
throw new Exception("Unknown object in postfix vector!");
}
}
if (operands.size() != 1) {
throw new Exception("Problem applying function");
}
Double result = ((Double)operands.pop());
if (result.isNaN() || result.isInfinite()) {
vals[vals.length-1] = Utils.missingValue();
} else {
vals[vals.length-1] = result.doubleValue();
}
}
/**
* Returns true if a token is an operator
* @param tok the token to check
* @return true if the supplied token is an operator
*/
private boolean isOperator(char tok) {
if (OPERATORS.indexOf(tok) == -1) {
return false;
}
return true;
}
/**
* Returns true if a token is a unary function
* @param tok the token to check
* @return true if the supplied token is a unary function
*/
private boolean isUnaryFunction(char tok) {
if (UNARY_FUNCTIONS.indexOf(tok) == -1) {
return false;
}
return true;
}
/**
* Return the infix priority of an operator
* @param opp the operator
* @return the infix priority
*/
private int infixPriority(char opp) {
switch (opp) {
case 'l' :
case 'b' :
case 'c' :
case 'e' :
case 's' :
case 'f' :
case 'h' :
case 'r' :
case 't' :
case 'n' :
return 3;
case '^' :
return 2;
case '*' :
return 2;
case '/' :
return 2;
case '+' :
return 1;
case '-' :
return 1;
case '(' :
return 4;
case ')' :
return 0;
default :
throw new IllegalArgumentException("Unrecognized operator:" + opp);
}
}
/**
* Return the stack priority of an operator
* @param opp the operator
* @return the stack priority
*/
private int stackPriority(char opp) {
switch (opp) {
case 'l' :
case 'b' :
case 'c' :
case 'e' :
case 's' :
case 'f' :
case 'h' :
case 'r' :
case 't' :
case 'n' :
return 3;
case '^' :
return 2;
case '*' :
return 2;
case '/' :
return 2;
case '+' :
return 1;
case '-' :
return 1;
case '(' :
return 0;
case ')' :
return -1;
default :
throw new IllegalArgumentException("Unrecognized operator:" + opp);
}
}
/**
* Return the postfix expression
*
* @return the postfix expression as a String
*/
public String getPostFixExpression() {
return m_postFixExpVector.toString();
}
public String toString() {
return m_originalInfix;
}
/**
* Returns the revision string.
*
* @return the revision
*/
public String getRevision() {
return RevisionUtils.extract("$Revision: 8034 $");
}
}