the node number of the tree, thx for your reply

[hywchina]

When I use XGB tree model, in a tree, the node number of the tree is continuous, some are discontinuous, may I ask why?

[trivialfis]

@hywchina Could you give an example output? Also a reproducible script with used XGBoost version?

[hywchina]

1. booster[104]:node4 is a leaf, and the nodes number are discontinuous;

2. booster[39]:node19 is a leaf, but the nodes number are continuous;

booster[104] and booster[39] from different trees

thank you very much

[trivialfis]

@hywchina I'm not sure I follow, did you mean the node number being a continuous sequence like 1, 2, 3, ..., 7, 8, 9?

That's related to how the tree updaters split (and prune) each node. Splitting at 1 then the two children will be 2, 3. Then split at 2, 4, 5 will become children of 2. The children of 3 will be 6, 7, assuming depth-wise splitting scheme. If pruner is used, the deleted node number will be reused for later splits.