Scikit Decision tree categorical features

问题

There is well-know problem in Tom's Mitchell Machine Learning book to build decision tree based on the following data, where Play ball is the target variable.

The resulting tree is following

I wonder whether it's possible to build this tree with scikit-learn. I found several examples where decision tree can be depicted as

export_graphviz(clf) 
Source(export_graphviz(clf, out_file=None))

However it looks like scikit doesn't work well with categorical data, the data has to be binarized into several columns. So as result, it is impossible to build the tree exactly as in the picture. Is it correct?

回答1:

Yes, it is correct that it is impossible to build such a tree with scikit-learn.

The primary reason is that this is a ternary tree (nodes with up to three children) but scikit-learn implements only binary trees - nodes have exactly two or no children:

cdef class Tree:
    """Array-based representation of a binary decision tree.
...

However, it is possible to get an equivalent binary tree of the form

Outlook == Sunny
    true  => Humidity == High
        true  => no
        false => yes      
    false => Outlook == Overcast
        true  => yes
        false => Wind == Strong
            true  => no
            false => yes 

来源：https://stackoverflow.com/questions/47586562/scikit-decision-tree-categorical-features