title: grid search random forests "RandomForestClassifier instance is not fitted yet"
body: <p>Im trying to do grid search on random forests classifier, I'm trying to test different PCA componenet and n_estimators</p>
  
  <pre><code>  model_rf = RandomForestClassifier()
    pca_rf = Pipeline([('pca', PCA()), ('rf', RandomForestClassifier())])
  
    param_grid_rf = [{
                  'pca__n_components': [20],
                  'rf__n_estimators': [5]
                  }]
  
    grid_cv_rf = GridSearchCV(estimator=pca_rf, cv=5,param_grid=param_grid_rf)
    grid_cv_rf.fit(x_train, y_train1)
    test_pca_evaluate = pca.transform(x_test)
    y_pred = model_rf.predict(test_pca_evaluate)#error here
  </code></pre>
  
  <p>In the last line I get an error "This RandomForestClassifier instance is not fitted yet. Call 'fit' with appropriate arguments before using this method."</p>