DOC: DataFrame.dropna doc-string examples

closes pandas-dev#15620

Author: jreback

pandas/core/frame.py

@@ -2714,6 +2714,11 @@ def lookup(self, row_labels, col_labels):
         col_labels : sequence
             The column labels to use for lookup
 
+        Returns
+        -------
+        values : ndarray
+            The found values
+
         Notes
         -----
         Akin to::
@@ -2722,11 +2727,6 @@ def lookup(self, row_labels, col_labels):
             for row, col in zip(row_labels, col_labels):
                 result.append(df.get_value(row, col))
 
-        Examples
-        --------
-        values : ndarray
-            The found values
-
         """
         n = len(row_labels)
         if n != len(col_labels):
@@ -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.