2.20 Booster lifecycle and config
A trained booster can be queried, sliced, reset, and round-tripped through its JSON config. This example trains eight rounds, then exercises booster-slice (take a contiguous range of rounds into a new booster), booster-config / booster-set-config! (serialize and restore the full configuration as JSON), booster-reset! (drop the boosted trees), and the booster-boosted-rounds / booster-num-feature queries.
(require ffi/vector json racket/port xgboost)
(provide run-example)
Helpers. A trained booster and a JSON-object check:
(define features (f32vector 1.0 2.0 0.5 2.0 1.0 1.5 3.0 0.5 0.0 0.5 3.0 2.0 4.0 2.0 1.0 1.5 1.5 0.5 2.5 3.5 1.5 0.0 1.0 0.0)) (define labels (f32vector 3.5 3.5 6.5 2.0 9.0 4.0 7.0 1.0)) (define (json-object? s) (hash? (with-input-from-string s read-json))) (define (make-trained-booster rounds) (define dm (make-dmatrix features #:nrow 8 #:ncol 3 #:missing -1.0 #:labels labels)) (values (train dm #:objective "reg:squarederror" #:max-depth 3 #:eta 0.1 #:verbosity 0 #:rounds rounds) dm))
The run. run-example returns the post-reset round count, the feature count, the sliced booster’s round count, and whether the config serializes to a JSON object:
(define (run-example) (define-values (booster dm) (make-trained-booster 8)) (define sliced (booster-slice booster 0 3)) (define config (booster-config booster)) (booster-set-config! (make-booster) config) (booster-reset! booster) (hash 'rounds (booster-boosted-rounds booster) 'features (booster-num-feature booster) 'sliced-rounds (booster-boosted-rounds sliced) 'config-json? (json-object? config)))
The harness "test/17-booster-lifecycle-config.rkt" prints these and asserts the slice kept 3 rounds, the matrix has 3 features, and the config is valid JSON.