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Created April 30, 2019 10:57
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import weka.core.Instances;
import weka.core.converters.ConverterUtils.DataSource;
import weka.filters.Filter;
import weka.filters.unsupervised.attribute.Add;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
public class wekaDev {
public static void main(String[] args) throws Exception {
// read in data
DataSource source = new DataSource("C:\\Program Files\\Weka-3-8\\data\\iris.arff");
Instances data = source.getDataSet();
// look at data before
System.out.println("\n====== BEFORE ======\n");
// make a list of random doubles
List<Double> list = new ArrayList<>(data.numInstances());
Random rand = new Random();
for (int i=0;i<=data.numInstances();i++) {
// get list of numbers into Instances object as new attribute
Add filter = new Add();
filter.setAttributeIndex("last"); // add as last so we know where it is
filter.setAttributeName("randomDouble"); // give it a name
filter.setInputFormat(data); // set the filter
data = Filter.useFilter(data, filter); // use the filter
// now update all the values
for (int i = 0; i < data.numInstances(); i++) {
data.instance(i).setValue(data.numAttributes()-1, list.get(i)); // need to -1 as zero based index
// look at data after
System.out.println("\n====== AFTER ======\n");
public static void printHead(Instances data, int n) {
int numCols = data.numAttributes();
for (int i=0; i<=(numCols-1); i++){
if (i < (numCols-1)) {
System.out.print(data.attribute(i).name() + ",");
else {
System.out.print(data.attribute(i).name() + "\n");
for (int i=0; i<=(n-1); i++){
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