Demo for accessing eval metrics in xgboost

demo/guide-python/evals_result.py

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+import xgboost as xgb
+##
+#  This script demonstrate how to access the eval metrics in xgboost
+##
+dtrain = xgb.DMatrix('../data/agaricus.txt.train', silent=True)
+dtest = xgb.DMatrix('../data/agaricus.txt.test', silent=True)
+
+param = [('max_depth', 2), ('objective', 'binary:logistic'), ('eval_metric', 'logloss'), ('eval_metric', 'error')]
+ 
+num_round = 2
+watchlist = [(dtest,'eval'), (dtrain,'train')]
+
+evals_result = {}
+bst = xgb.train(param, dtrain, num_round, watchlist, evals_result=evals_result)
+
+print('Access logloss metric directly from evals_result:')
+print(evals_result['eval']['logloss'])
+
+print('')
+print('Access metrics through a loop:')
+for e_name, e_mtrs in evals_result.items():
+    print('- {}'.format(e_name))
+    for e_mtr_name, e_mtr_vals in e_mtrs.items():
+        print('   - {}'.format(e_mtr_name))
+        print('      - {}'.format(e_mtr_vals))
+
+print('')
+print('Access complete dictionary:')
+print(evals_result)