Tue Oct 06, 2009 8:52 am
http://www.run.montefiore.ulg.ac.be/~francois/software/jaDTi/http://www.scribd.com/doc/2062526/Decision-Tree-Algorithmimport java.io.*;
import java.util.*;
public class ID3
{
int numAttributes;
String []attributeNames;
Vector []domains;
/* The class to represent a data point consisting of numAttributes values
of attributes */
class DataPoint {
public int []attributes;
public DataPoint(int numattributes) {
attributes = new int[numattributes];
}
};
/* The class to represent a node in the decomposition tree.
*/
class TreeNode {
public double entropy;
public Vector data;
public int decompositionAttribute;
public int decompositionValue;
public TreeNode []children;
public TreeNode parent;
public TreeNode() {
data = new Vector();
}
};
TreeNode root = new TreeNode();
public int getSymbolValue(int attribute, String symbol) {
int index = domains[attribute].indexOf(symbol);
if (index < 0) {
domains[attribute].addElement(symbol);
return domains[attribute].size() -1;
}
return index;
}
public int []getAllValues(Vector data, int attribute) {
Vector values = new Vector();
int num = data.size();
for (int i=0; i< num; i++) {
DataPoint point = (DataPoint)data.elementAt(i);
String symbol =
(String)domains[attribute].elementAt(point.attributes[attribute] );
int index = values.indexOf(symbol);
if (index < 0) {
values.addElement(symbol);
}
}
int []array = new int[values.size()];
for (int i=0; i< array.length; i++) {
String symbol = (String)values.elementAt(i);
array = domains[attribute].indexOf(symbol);
}
values = null;
return array;
}
public Vector getSubset(Vector data, int attribute, int value) {
Vector subset = new Vector();
int num = data.size();
for (int i=0; i< num; i++) {
DataPoint point = (DataPoint)data.elementAt(i);
if (point.attributes[attribute] == value) subset.addElement(point);
}
return subset;
}
public double calculateEntropy(Vector data) {
int numdata = data.size();
if (numdata == 0) return 0;
int attribute = numAttributes-1;
int numvalues = domains[attribute].size();
double sum = 0;
for (int i=0; i< numvalues; i++) {
int count=0;
for (int j=0; j< numdata; j++) {
DataPoint point = (DataPoint)data.elementAt(j);
if (point.attributes[attribute] == i) count++;
}
double probability = 1.*count/numdata;
if (count > 0) sum += -probability*Math.log(probability);
}
return sum;
}
public boolean alreadyUsedToDecompose(TreeNode node, int attribute) {
if (node.children != null) {
if (node.decompositionAttribute == attribute )
return true;
}
if (node.parent == null) return false;
return alreadyUsedToDecompose(node.parent, attribute);
}
public void decomposeNode(TreeNode node) {
double bestEntropy=0;
boolean selected=false;
int selectedAttribute=0;
int numdata = node.data.size();
int numinputattributes = numAttributes-1;
node.entropy = calculateEntropy(node.data);
if (node.entropy == 0) return;
for (int i=0; i< numinputattributes; i++) {
int numvalues = domains.size();
if ( alreadyUsedToDecompose(node, i) ) continue;
double averageentropy = 0;
for (int j=0; j< numvalues; j++) {
Vector subset = getSubset(node.data, i, j);
if (subset.size() == 0) continue;
double subentropy = calculateEntropy(subset);
averageentropy += subentropy *
subset.size();
}
averageentropy = averageentropy / numdata; //
Taking the weighted average
if (selected == false) {
selected = true;
bestEntropy = averageentropy;
selectedAttribute = i;
} else {
if (averageentropy < bestEntropy) {
selected = true;
bestEntropy = averageentropy;
selectedAttribute = i;
}
}
}
if (selected == false) return;
int numvalues = domains[selectedAttribute].size();
node.decompositionAttribute = selectedAttribute;
node.children = new TreeNode [numvalues];
for (int j=0; j< numvalues; j++) {
node.children[j] = new TreeNode();
node.children[j].parent = node;
node.children[j].data = getSubset(node.data,
selectedAttribute, j);
node.children[j].decompositionValue = j;
}
for (int j=0; j< numvalues; j++) {
decomposeNode(node.children[j]);
}
node.data = null;
}
public int readData(String filename) throws Exception {
FileInputStream in = null;
try {
File inputFile = new File(filename);
in = new FileInputStream(inputFile);
} catch ( Exception e) {
System.err.println( "Unable to open data file: " + filename + "\n" + e);
return 0;
}
BufferedReader bin = new BufferedReader(new InputStreamReader(in) );
String input;
while(true) {
input = bin.readLine();
if (input == null) {
System.err.println( "No data found in the data file: " + filename +
"\n");
return 0;
}
if (input.startsWith("//")) continue;
if (input.equals("")) continue;
break;
}
StringTokenizer tokenizer = new StringTokenizer(input);
numAttributes = tokenizer.countTokens();
if (numAttributes <= 1) {
System.err.println( "Read line: " + input);
System.err.println( "Could not obtain the names of attributes in the
line");
System.err.println( "Expecting at least one input attribute and one
output attribute");
return 0;
}
domains = new Vector[numAttributes];
for (int i=0; i < numAttributes; i++) domains = new Vector();
attributeNames = new String[numAttributes];
for (int i=0; i < numAttributes; i++) {
attributeNames = tokenizer.nextToken();
}
while(true) {
input = bin.readLine();
if (input == null) break;
if (input.startsWith("//")) continue;
if (input.equals("")) continue;
tokenizer = new StringTokenizer(input);
int numtokens = tokenizer.countTokens();
if (numtokens != numAttributes) {
System.err.println( "Read " + root.data.size() + " data");
System.err.println( "Last line read: " + input);
System.err.println( "Expecting " + numAttributes + " attributes");
return 0;
}
DataPoint point = new DataPoint(numAttributes);
for (int i=0; i < numAttributes; i++) {
point.attributes = getSymbolValue(i, tokenizer.nextToken()
);
}
root.data.addElement(point);
}
bin.close();
return 1;
}
public void printTree(TreeNode node, String tab) {
int outputattr = numAttributes-1;
if (node.children == null) {
int []values = getAllValues(node.data, outputattr );
if (values.length == 1) {
System.out.println(tab + "\t" + attributeNames[outputattr] + " = \"" +
domains[outputattr].elementAt(values[0]) + "\";");
return;
}
System.out.print(tab + "\t" + attributeNames[outputattr] + " = {");
for (int i=0; i < values.length; i++) {
System.out.print("\"" + domains[outputattr].elementAt(values) + "\"
");
if ( i != values.length-1 ) System.out.print( " , " );
}
System.out.println( " };");
return;
}
int numvalues = node.children.length;
for (int i=0; i < numvalues; i++) {
System.out.println(tab + "if( " +
attributeNames[node.decompositionAttribute] + " == \"" +
domains[node.decompositionAttribute].elementAt(i)
+ "\") {" );
printTree(node.children, tab + "\t");
if (i != numvalues-1) System.out.print(tab + "} else ");
else System.out.println(tab + "}");
}
}
public void createDecisionTree() {
decomposeNode(root);
printTree(root, "");
}
/* main function */
public static void main(String[] args) throws Exception {
ID3 me = new ID3();
int status = me.readData("c:\\in.txt");
if (status <= 0) return;
me.createDecisionTree();
}
}
Wed Aug 25, 2010 11:53 pm
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