20.27 Rules Using Rpart Plot

We can also use rpart.plot::rpart.rules() from Stephen Milborrow’s excellent rpart.plot (Milborrow 2026) package. This will convert the decision tree into rules:

rpart.rules(model)

##  rain_tomorrow                                                      
##           0.14 when humidity_3pm <  72                              
##           0.36 when humidity_3pm is 72 to 83 & wind_gust_speed <  42
##           0.60 when humidity_3pm is 72 to 83 & wind_gust_speed >= 42
##           0.77 when humidity_3pm >=       83

Some variations appear below. The first adds the coverage of the rule, which is the percentage of the training dataset that ends up in this part of the decision tree. The second adds the proportions of observations within a leaf node that correspond to No/Yes.

rpart.rules(model, cover=TRUE)

##  rain_tomorrow                                                         cover
##           0.14 when humidity_3pm <  72                                   83%
##           0.36 when humidity_3pm is 72 to 83 & wind_gust_speed <  42      5%
##           0.60 when humidity_3pm is 72 to 83 & wind_gust_speed >= 42      4%
##           0.77 when humidity_3pm >=       83                              7%

rpart.rules(model, extra=4)

##  rain_tomorrow   No Yes                                                       
##             No [.86 .14] when humidity_3pm <  72                              
##             No [.64 .36] when humidity_3pm is 72 to 83 & wind_gust_speed <  42
##            Yes [.40 .60] when humidity_3pm is 72 to 83 & wind_gust_speed >= 42
##            Yes [.23 .77] when humidity_3pm >=       83

We can even obtain an explanation of the rules used in a prediction. Here we select specific observations to obtain the prediction and the rule used to make that prediction.

rpart.predict(model, newdata=ds[c(10, 12, 17), vars], rules=TRUE)

##          No       Yes                                                         
## 1 0.8626962 0.1373038 because humidity_3pm <  72                              
## 2 0.2279167 0.7720833 because humidity_3pm >=       83                        
## 3 0.6350854 0.3649146 because humidity_3pm is 72 to 83 & wind_gust_speed <  42

References

Milborrow, Stephen. 2026. Rpart.plot: Plot Rpart Models: An Enhanced Version of Plot.rpart. http://www.milbo.org/rpart-plot/index.html.

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