DOC: DataFrame.dropna doc-string examples

closes pandas-dev#15620

Author: jreback

pandas/core/frame.py

@@ -3084,6 +3084,46 @@ def dropna(self, axis=0, how='any', thresh=None, subset=None,
         Returns
         -------
         dropped : DataFrame
+
+        Examples
+        --------
+        >>> df = pd.DataFrame([[np.nan, 2, np.nan, 0], [3, 4, np.nan, 1],
+                               [np.nan, np.nan, np.nan, 5]],
+                              columns=list('ABCD'))
+        >>> df
+        >>>     A    B   C    D
+            0   NaN  2.0 NaN  0
+            1   3.0  4.0 NaN  1
+            2   NaN  NaN NaN  5
+
+        Drop the columns where all elements are nan
+        >>> df.dropna(axis=1, how='all')
+        >>>     A   B    D
+            0  NaN  2.0  0
+            1  3.0  4.0  1
+            2  NaN  NaN  5
+
+        Drop the columns where any of the elements is nan
+        >>> df.dropna(axis=1, how='any')
+        >>>    D
+            0  0
+            1  1
+            2  5
+
+        Drop the rows where all of the elements is nan
+        (there is no row to drop, so df stays the same)
+        >>> df.dropna(axis=0, how='all')
+        >>>     A    B   C    D
+            0   NaN  2.0 NaN  0
+            1   3.0  4.0 NaN  1
+            2   NaN  NaN NaN  5
+
+        Keep only the rows with at least 2 non-na values
+        >>> df.dropna(thresh=2)
+        >>>    A    B     C    D
+            0  NaN  2.0   NaN  0
+            1  3.0  4.0   NaN  1
+
         """
         inplace = validate_bool_kwarg(inplace, 'inplace')
         if isinstance(axis, (tuple, list)):
@@ -3966,7 +4006,7 @@ def stack(self, level=-1, dropna=True):
             values
 
         Examples
-        ----------
+        --------
         >>> s
              a   b
         one  1.  2.