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I am trying to use the J48 algorithm in Weka for my classification problem. However, Weka is displaying weird results for precision and F-measure, it is showing a question mark '?' instead of any number. Anyone knows how can I fix this ?enter image description here

Rajnish Kumar Jha
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Weka could not calculate statistics for class secondary_hypothyroid as no instance is classified as secondary_hypothyroid. See How to interpret weka classification? for details.

hkn
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Welcome to SO. F-measure is the harmonic mean of precision and recall values. It allows to evaluate P and R together. It is calculated as follows.

enter image description here

Precision and Recall values are derived from data of at least two classes. If your data does not meet this requirement, "?" you can see the sign. When creating class names, you may not have paid attention to case separation. I recommend checking the class names. Also, the calculation may be corrupted due to a non-numeric character that was overlooked in the data while calculating the P and R values. I suggest you check all your data. If you give a summary of the data you have, we can make more useful suggestions. Good luck.

NCC1701
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