Print gbm tree components

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.

Usage

# S3 method for class 'gbm.tree'
pretty(object, i.tree = 1)

Arguments

object

a gbm.object initially fit using gbm

i.tree

the index of the tree component to extract from object and display

Value

pretty.gbm.tree returns a data frame. Each row corresponds to a node in the tree. Columns indicate

SplitVar

index of which variable is used to split. -1 indicates a terminal node.

SplitCodePred

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.

LeftNode

the index of the row corresponding to the left node.

RightNode

the index of the row corresponding to the right node.

ErrorReduction

the reduction in the loss function as a result of splitting this node.

Weight

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.

See also

gbm, gbm.object

Author

Greg Ridgeway gregridgeway@gmail.com