title: GridSearchCV - FitFailedWarning: Estimator fit failed
body: <p>I am running this:</p>
  
  <pre><code># Hyperparameter tuning - Random Forest #
  
  # Hyperparameters' grid
  parameters = {'n_estimators': list(range(100, 250, 25)), 'criterion': ['gini', 'entropy'], 
                'max_depth': list(range(2, 11, 2)), 'max_features': [0.1, 0.2, 0.3, 0.4, 0.5], 
                'class_weight': [{0: 1, 1: i} for i in np.arange(1, 4, 0.2).tolist()], 'min_samples_split': list(range(2, 7))}
  
  
  # Instantiate random forest
  from sklearn.ensemble import RandomForestClassifier
  classifier = RandomForestClassifier(random_state=0)
  
  
  # Execute grid search and retrieve the best classifier
  from sklearn.model_selection import GridSearchCV
  classifiers_grid = GridSearchCV(estimator=classifier, param_grid=parameters, scoring='balanced_accuracy',
                                     cv=5, refit=True, n_jobs=-1)
  classifiers_grid.fit(X, y)
  </code></pre>
  
  <p>and I am receiving this warning:</p>
  
  <pre><code>.../anaconda/lib/python3.7/site-packages/sklearn/model_selection/_validation.py:536: 
  FitFailedWarning: Estimator fit failed. The score on this train-test partition for these parameters will be set to nan. Details: 
  TypeError: '&lt;' not supported between instances of 'str' and 'int'
  </code></pre>
  
  <p>Why is this and how can I fix it?</p>