DOC add versionadded versionchanged for 0.21 (scikit-learn#16737)

Co-authored-by: Mateusz Górski <[email protected]>
Co-authored-by: Nicolas Hug <[email protected]>
Co-authored-by: Thomas J Fan <[email protected]>

Author: 4 people

sklearn/cluster/_agglomerative.py

@@ -763,6 +763,9 @@ class AgglomerativeClustering(ClusterMixin, BaseEstimator):
     n_connected_components_ : int
         The estimated number of connected components in the graph.
 
+        .. versionadded:: 0.21
+            ``n_connected_components_`` was added to replace ``n_components_``.
+
     children_ : array-like of shape (n_samples-1, 2)
         The children of each non-leaf node. Values less than `n_samples`
         correspond to leaves of the tree which are the original samples.
@@ -1007,6 +1010,9 @@ class FeatureAgglomeration(AgglomerativeClustering, AgglomerationTransform):
     n_connected_components_ : int
         The estimated number of connected components in the graph.
 
+        .. versionadded:: 0.21
+            ``n_connected_components_`` was added to replace ``n_components_``.
+
     children_ : array-like of shape (n_nodes-1, 2)
         The children of each non-leaf node. Values less than `n_features`
         correspond to leaves of the tree which are the original samples.

sklearn/ensemble/_voting.py

@@ -125,6 +125,9 @@ class VotingClassifier(ClassifierMixin, _BaseVoting):
         ``self.estimators_``. An estimator can be set to ``'drop'``
         using ``set_params``.
 
+        .. versionchanged:: 0.21
+            ``'drop'`` is accepted.
+
         .. deprecated:: 0.22
            Using ``None`` to drop an estimator is deprecated in 0.22 and
            support will be dropped in 0.24. Use the string ``'drop'`` instead.
@@ -372,6 +375,9 @@ class VotingRegressor(RegressorMixin, _BaseVoting):
         ``self.estimators_``. An estimator can be set to ``'drop'`` using
         ``set_params``.
 
+        .. versionchanged:: 0.21
+            ``'drop'`` is accepted.
+
         .. deprecated:: 0.22
            Using ``None`` to drop an estimator is deprecated in 0.22 and
            support will be dropped in 0.24. Use the string ``'drop'`` instead.