Update documentation

Author: timsaucer

docs/source/user-guide/common-operations/expressions.rst

@@ -82,6 +82,13 @@ approaches.
     Indexing an element of an array via ``[]`` starts at index 0 whereas
     :py:func:`~datafusion.functions.array_element` starts at index 1.
 
+Starting in DataFusion 49.0.0 you can also create slices of array elements using
+slice syntax from Python.
+
+.. ipython:: python
+
+    df.select(col("a")[1:3].alias("second_two_elements"))
+
 To check if an array is empty, you can use the function :py:func:`datafusion.functions.array_empty` or `datafusion.functions.empty`.
 This function returns a boolean indicating whether the array is empty.
 

python/datafusion/expr.py

@@ -357,7 +357,12 @@ def __getitem__(self, key: str | int | slice) -> Expr:
 
         If ``key`` is a string, returns the subfield of the struct.
         If ``key`` is an integer, retrieves the element in the array. Note that the
-        element index begins at ``0``, unlike `array_element` which begins at ``1``.
+        element index begins at ``0``, unlike
+        :py:func:`~datafusion.functions.array_element` which begins at ``1``.
+        If ``key`` is a slice, returns an array that contains a slice of the
+        original array. Similar to integer indexing, this follows Python convention
+        where the index begins at ``0`` unlike
+        :py:func:`~datafusion.functions.array_slice` which begins at ``1``.
         """
         if isinstance(key, int):
             return Expr(

python/datafusion/functions.py

@@ -2655,7 +2655,7 @@ def cume_dist(
     """Create a cumulative distribution window function.
 
     This window function is similar to :py:func:`rank` except that the returned values
-    are the ratio of the row number to the total numebr of rows. Here is an example of a
+    are the ratio of the row number to the total number of rows. Here is an example of a
     dataframe with a window ordered by descending ``points`` and the associated
     cumulative distribution::