title: I keep getting AttributeError in RandomSearchCV
body: <pre><code>x_tu = data_cls_tu.iloc[:,1:].values
  y_tu = data_cls_tu.iloc[:,0].values
  
  classifier = DecisionTreeClassifier()
  parameters = [{"max_depth": [3,None],
                 "min_samples_leaf": np.random.randint(1,9),
                 "criterion": ["gini","entropy"]}]
  randomcv = RandomizedSearchCV(estimator=classifier, param_distributions=parameters,
                                scoring='accuracy', cv=10, n_jobs=-1,
                                random_state=0)
  randomcv.fit(x_tu, y_tu)
  
  
  
  ---------------------------------------------------------------------------
  AttributeError                            Traceback (most recent call last)
  &lt;ipython-input-17-fa8376cb54b8&gt; in &lt;module&gt;()
       11                               scoring='accuracy', cv=10, n_jobs=-1,
       12                               random_state=0)
  ---&gt; 13 randomcv.fit(x_tu, y_tu)
  
  ~\Anaconda3\lib\site-packages\sklearn\model_selection\_search.py in fit(self, X, y, groups, **fit_params)
      616         n_splits = cv.get_n_splits(X, y, groups)
      617         # Regenerate parameter iterable for each fit
  --&gt; 618         candidate_params = list(self._get_param_iterator())
      619         n_candidates = len(candidate_params)
      620         if self.verbose &gt; 0:
  
  ~\Anaconda3\lib\site-packages\sklearn\model_selection\_search.py in __iter__(self)
      236         # in this case we want to sample without replacement
      237         all_lists = np.all([not hasattr(v, "rvs")
  --&gt; 238                             for v in self.param_distributions.values()])
      239         rnd = check_random_state(self.random_state)
      240 
  
  AttributeError: 'list' object has no attribute 'values'
  </code></pre>
  
  <p>Hi, I keep getting error on the fit method for RandomSearchCV.</p>
  
  <p>It worked when I used them on GridSearchCV, but GridSearchCV took 5 hours to complete.</p>
  
  <p>x_tu, y_tu are both numpy.ndarray type.</p>