gbm stores the collection of trees used to construct the model in a
compact matrix structure. This function extracts the information from a
single tree and displays it in a slightly more readable form. This function
is mostly for debugging purposes and to satisfy some users' curiosity.
# S3 method for gbm.tree
pretty(object, i.tree = 1)a gbm.object initially fit using
gbm
the index of the tree component to extract from object
and display
pretty.gbm.tree returns a data frame. Each row corresponds to
a node in the tree. Columns indicate
index of which variable is used to split. -1 indicates a terminal node.
if the
split variable is continuous then this component is the split point. If the
split variable is categorical then this component contains the index of
object$c.split that describes the categorical split. If the node is a
terminal node then this is the prediction.
the index of the row corresponding to the left node.
the index of the row corresponding to the right node.
the reduction in the loss function as a result of splitting this node.
the total weight of observations in the node. If weights are all equal to 1 then this is the number of observations in the node.