Weka J48更换选项 - 没有区别

Question

I am trying to change options for J48 classifier, but it makes no difference in the resulted tree.

My code:

J48 cls = new J48();
Instances data = new Instances(new BufferedReader(new FileReader("someArffFile")));
data.setClassIndex(data.numAttributes() - 1);

//was trying to use -M 1 and -M 5, but no difference    
String[] options = new String[1];
options[0] = "-C 1.0 –M 1";     
cls.setOptions(options);

cls.buildClassifier(data);

//displaying J48 tree
TreeVisualizer tv = new TreeVisualizer(null,cls.graph(),new PlaceNode2());

After I set the value with this method then everything is working fine.

cls.setMinNumObj(5);

Any ideas how I can use setOptions method instead of setMinNumObj?

Answer 1

The problem is how you try to set the options. The options array should be like the args array in the main method, one string per element:

String[] options = {"-C", "1.0", "–M", "1"};
cls.setOptions(options);

Otherwise it won't work.

Answer 2

First, options should be an array rather than a string. So you can try sth as follows.

String[] options = {"-C", "1.0", "-M", "1"};
cls.setOptions(options);

More important, a small bug should be noticed carefully. Both in your question and in the previous answer from @Sentry, a shorter line happens before C, like "-C"; but a longer line happens before M, like "–M".

If you watch carefully, you will find that the signs before M is actually not the minus sign because it's longer than minus sign. When you change the longer line into a really minus sign, you could get a right result by the codes above.

Good luck.

Answer 3

The best way is to utilize the splitOptions(String[] options) method of the weka.Core.Utils class :

String[] options = weka.core.Utils.splitOptions("-C 1.0 –M 1");
cls.setOptions(options);