Internal node predictions of xgboost model - xgboost

Question

Is it possible to calculate the internal node predictions of an xgboost model? The R package, gbm, provides a prediction for internal nodes of each tree.
The xgboost output, however only shows predictions for the final leaves of the model.
xgboost output:
Notice that the Quality column has the final prediction for the leaf node in row 6. I would like that value for each of the internal nodes as well.
Tree Node ID Feature Split Yes No Missing Quality Cover
1: 0 0 0-0 Sex=female 0.50000 0-1 0-2 0-1 246.6042790 222.75
2: 0 1 0-1 Age 13.00000 0-3 0-4 0-4 22.3424225 144.25
3: 0 2 0-2 Pclass=3 0.50000 0-5 0-6 0-5 60.1275253 78.50
4: 0 3 0-3 SibSp 2.50000 0-7 0-8 0-7 23.6302433 9.25
5: 0 4 0-4 Fare 26.26875 0-9 0-10 0-9 21.4425507 135.00
6: 0 5 0-5 Leaf NA <NA> <NA> <NA> 0.1747126 42.50
R gbm output:
In the R gbm package output, the prediction column contains values for both leaf nodes (SplitVar == -1) and the internal nodes. I would like access to these values from the xgboost model
SplitVar SplitCodePred LeftNode RightNode MissingNode ErrorReduction Weight Prediction
0 1 0.000000000 1 8 15 32.564591 445 0.001132514
1 2 9.500000000 2 3 7 3.844470 282 -0.085827382
2 -1 0.119585850 -1 -1 -1 0.000000 15 0.119585850
3 0 1.000000000 4 5 6 3.047926 207 -0.092846157
4 -1 -0.118731665 -1 -1 -1 0.000000 165 -0.118731665
5 -1 0.008846912 -1 -1 -1 0.000000 42 0.008846912
6 -1 -0.092846157 -1 -1 -1 0.000000 207 -0.092846157
Question:
How do I access or calculate predictions for the internal nodes of an xgboost model? I would like to use them for a greedy, poor man's version of SHAP scores.

Answer 1

The solution to this problem is to dump the xgboost json object with all_stats=True. That adds the cover statistic to the output which can be used to distribute the leaf points through the internal nodes:
def _calculate_contribution(node: AnyNode) -> float32:
if isinstance(node, Leaf):
return node.contrib
else:
return (
node.left.cover * Node._calculate_contribution(node.left)
+ node.right.cover * Node._calculate_contribution(node.right)
) / node.cover
The internal contribution is the weighted average of the child contributions. Using this method, the generated results exactly match those returned when calling the predict method with pred_contribs=True and approx_contribs=True.