sklearn use RandomizedSearchCV with custom metrics and catch Exceptions

问题

I am using the RandomizedSearchCV function in sklearn with a Random Forest Classifier. To see different metrics i am using a custom scoring

from sklearn.metrics import make_scorer, roc_auc_score, recall_score, matthews_corrcoef, balanced_accuracy_score, accuracy_score

acc = make_scorer(accuracy_score)

auc_score = make_scorer(roc_auc_score)
recall = make_scorer(recall_score)
mcc = make_scorer(matthews_corrcoef)
bal_acc = make_scorer(balanced_accuracy_score)

scoring = {"roc_auc_score": auc_score, "recall": recall, "MCC" : mcc, 'Bal_acc' : bal_acc, "Accuracy": acc }

these Custom scorers are the used for the Randomized search

rf_random = RandomizedSearchCV(estimator=rf, param_distributions=random_grid, n_iter=100, cv=split, verbose=2,
                               random_state=42, n_jobs=-1, error_score=np.nan, scoring = scoring, iid = True, refit="roc_auc_score")

Now the problem is, as I am using custom splits, the AUC is throwing an exception because there is only one class label for this exact split.

I do not want to change the splits, hence is there a possibility to catch these exceptions within the RandomizedSearchCV or the make_scorer functions? So e.g. if one of the metrics is not calculated (due to an exception) just put in NaN and go on with the next model.

Edit: Apparently the error_score excepts model training but not the metric calculation. If I use eg Accuracy everything works and I just get the warnings in the folds where I have only one class label. If I use eg AUC as Metric I still get the exceptions thrown.

Would be great to get some ideas here!

Solution: Define a custom scorer with exception:

def custom_scorer(y_true, y_pred, actual_scorer):
score = np.nan

try:
  score = actual_scorer(y_true, y_pred)
except ValueError: 
  pass

return score

This leads to a new metric:

acc = make_scorer(accuracy_score)
recall = make_scorer(custom_scorer, actual_scorer=recall_score)
new_auc = make_scorer(custom_scorer, actual_scorer=roc_auc_score)
mcc = make_scorer(custom_scorer, actual_scorer=matthews_corrcoef)
bal_acc = make_scorer(custom_scorer,actual_scorer=balanced_accuracy_score)

scoring = {"roc_auc_score": new_auc, "recall": recall, "MCC" : mcc, 'Bal_acc' : bal_acc, "Accuracy": acc }

Which in turn can be passed to the scoring parameter of RandomizedSearchCV

A second solution I found was :

def custom_auc(clf, X, y_true):
score = np.nan
y_pred = clf.predict_proba(X)
try:
    score = roc_auc_score(y_true, y_pred[:, 1])
except Exception:
    pass

return score

which also can be passed to the scoring argument:

scoring = {"roc_auc_score": custom_auc, "recall": recall, "MCC" : mcc, 'Bal_acc' : bal_acc, "Accuracy": acc }

(Adapted from this answer)

回答1:

You can have a generic scorer which can take other scorers as input, check the results, catch any exceptions they throw and return a fixed value on them.

def custom_scorer(y_true, y_pred, actual_scorer):
    score = np.nan

    try:
      score = actual_scorer(y_true, y_pred)
    except Exception: 
      pass

    return score

Then you can call this using:

acc = make_scorer(custom_scorer, actual_scorer = accuracy_score)
auc_score = make_scorer(custom_scorer, actual_scorer = roc_auc_score, 
                        needs_threshold=True) # <== Added this to get correct roc
recall = make_scorer(custom_scorer, actual_scorer = recall_score)
mcc = make_scorer(custom_scorer, actual_scorer = matthews_corrcoef)
bal_acc = make_scorer(custom_scorer, actual_scorer = balanced_accuracy_score)

Example to reproduce:

import numpy as np
def custom_scorer(y_true, y_pred, actual_scorer):
    score = np.nan

    try:
      score = actual_scorer(y_true, y_pred)
    except Exception: 
      pass

    return score


from sklearn.metrics import make_scorer, roc_auc_score, accuracy_score
acc = make_scorer(custom_scorer, actual_scorer = accuracy_score)
auc_score = make_scorer(custom_scorer, actual_scorer = roc_auc_score, 
                        needs_threshold=True) # <== Added this to get correct roc

from sklearn.datasets import load_iris
X, y = load_iris().data, load_iris().target

from sklearn.tree import DecisionTreeClassifier
from sklearn.model_selection import GridSearchCV, KFold
cvv = KFold(3)
params={'criterion':['gini', 'entropy']}
gc = GridSearchCV(DecisionTreeClassifier(), param_grid=params, cv =cvv, 
                  scoring={"roc_auc": auc_score, "accuracy": acc}, 
                  refit="roc_auc", n_jobs=-1, 
                  return_train_score = True, iid=False)
gc.fit(X, y)
print(gc.cv_results_)

来源：https://stackoverflow.com/questions/53705966/sklearn-use-randomizedsearchcv-with-custom-metrics-and-catch-exceptions