DOC:Improve the docstring of DataFrame.iloc() (pandas-dev#20228)

Author: tuhinmahmud

pandas/core/indexing.py

@@ -1924,7 +1924,8 @@ def _getitem_axis(self, key, axis=None):
 
 
 class _iLocIndexer(_LocationIndexer):
-    """Purely integer-location based indexing for selection by position.
+    """
+    Purely integer-location based indexing for selection by position.
 
     ``.iloc[]`` is primarily integer position based (from ``0`` to
     ``length-1`` of the axis), but may also be used with a boolean
@@ -1937,14 +1938,125 @@ class _iLocIndexer(_LocationIndexer):
     - A slice object with ints, e.g. ``1:7``.
     - A boolean array.
     - A ``callable`` function with one argument (the calling Series, DataFrame
-      or Panel) and that returns valid output for indexing (one of the above)
+      or Panel) and that returns valid output for indexing (one of the above).
+      This is useful in method chains, when you don't have a reference to the
+      calling object, but would like to base your selection on some value.
 
     ``.iloc`` will raise ``IndexError`` if a requested indexer is
     out-of-bounds, except *slice* indexers which allow out-of-bounds
     indexing (this conforms with python/numpy *slice* semantics).
 
-    See more at :ref:`Selection by Position <indexing.integer>`
+    See more at ref:`Selection by Position <indexing.integer>`.
+
+    See Also
+    --------
+    DataFrame.iat : Fast integer location scalar accessor.
+    DataFrame.loc : Purely label-location based indexer for selection by label.
+    Series.iloc : Purely integer-location based indexing for
+                   selection by position.
+
+    Examples
+    --------
+
+    >>> mydict = [{'a': 1, 'b': 2, 'c': 3, 'd': 4},
+    ...           {'a': 100, 'b': 200, 'c': 300, 'd': 400},
+    ...           {'a': 1000, 'b': 2000, 'c': 3000, 'd': 4000 }]
+    >>> df = pd.DataFrame(mydict)
+    >>> df
+          a     b     c     d
+    0     1     2     3     4
+    1   100   200   300   400
+    2  1000  2000  3000  4000
+
+    **Indexing just the rows**
+
+    With a scalar integer.
+
+    >>> type(df.iloc[0])
+    <class 'pandas.core.series.Series'>
+    >>> df.iloc[0]
+    a    1
+    b    2
+    c    3
+    d    4
+    Name: 0, dtype: int64
+
+    With a list of integers.
+
+    >>> df.iloc[[0]]
+       a  b  c  d
+    0  1  2  3  4
+    >>> type(df.iloc[[0]])
+    <class 'pandas.core.frame.DataFrame'>
+
+    >>> df.iloc[[0, 1]]
+         a    b    c    d
+    0    1    2    3    4
+    1  100  200  300  400
+
+    With a `slice` object.
+
+    >>> df.iloc[:3]
+          a     b     c     d
+    0     1     2     3     4
+    1   100   200   300   400
+    2  1000  2000  3000  4000
+
+    With a boolean mask the same length as the index.
+
+    >>> df.iloc[[True, False, True]]
+          a     b     c     d
+    0     1     2     3     4
+    2  1000  2000  3000  4000
+
+    With a callable, useful in method chains. The `x` passed
+    to the ``lambda`` is the DataFrame being sliced. This selects
+    the rows whose index label even.
+
+    >>> df.iloc[lambda x: x.index % 2 == 0]
+          a     b     c     d
+    0     1     2     3     4
+    2  1000  2000  3000  4000
+
+    **Indexing both axes**
+
+    You can mix the indexer types for the index and columns. Use ``:`` to
+    select the entire axis.
+
+    With scalar integers.
+
+    >>> df.iloc[0, 1]
+    2
+
+    With lists of integers.
+
+    >>> df.iloc[[0, 2], [1, 3]]
+          b     d
+    0     2     4
+    2  2000  4000
+
+    With `slice` objects.
+
+    >>> df.iloc[1:3, 0:3]
+          a     b     c
+    1   100   200   300
+    2  1000  2000  3000
+
+    With a boolean array whose length matches the columns.
+
+    >>> df.iloc[:, [True, False, True, False]]
+          a     c
+    0     1     3
+    1   100   300
+    2  1000  3000
+
+    With a callable function that expects the Series or DataFrame.
 
+    >>> df.iloc[:, lambda df: [0, 2]]
+          a     c
+    0     1     3
+    1   100   300
+    2  1000  3000
     """
 
     _valid_types = ("integer, integer slice (START point is INCLUDED, END "