What+do+those+numbers+mean+in+a+J48+tree?

= What do those numbers mean in a J48 tree? =

The **first** number is the total number of instances (weight of instances) reaching the leaf. The **second** number is the number (weight) of those instances that are misclassified.

If your data has **missing** attribute values then you will end up with **fractional** instances at the leafs. When splitting on an attribute where some of the training instances have missing values, J48 will divide a training instance with a missing value for the split attribute up into fractional parts proportional to the frequencies of the observed non-missing values. This is discussed in the Witten & Frank Data Mining book as well as Ross Quinlan's original publications on C4.5.

Taken from the following Wekalist posts:
 * [|meaning of first/second number]
 * [|fractional numbers]