Confusion matrix in Weka

Question

I want to calculate confusion matrix, f1 score, roc etc. But the Weka output is showing this. How can I get the confusion matrix, f1 score, roc, etc?

Answer 1

First of all, your dataset seems to have a numeric class attribute. Correlation coefficient is a statistic generated for regression models. A confusion matrix (which you want) is only computed for classification models.

Secondly, you are using ZeroR as classifier, which is not a very useful classifier (only for determining a baseline). ZeroR either predicts the mean class value (numeric class attribute) or the majority class (nominal class attribute).

Solutions:

1. Ensure that you are using the right attribute for your class. Assuming that you are using the Weka Explorer, check the combobox on the Classify panel that it has the right attribute selected. On the command-line, use the -c flag to specify the index of the class attribute (1-based index, first and last can be used as well).
2. If you imported your data from a CSV file and the class attribute column contains only numeric values, then Weka will have left it as numeric (it doesn't know that this column represents a nominal attribute). In that case, make sure that you convert your class attribute to a nominal one, e.g., by using the NumericToNominal filter in the Preprocess panel.
3. Choose a different classifier, like RandomForest or J48, which tend to generate reasonable models with just the default parameters.