jorisvandenbossche commented on code in PR #33925:
URL: https://github.com/apache/arrow/pull/33925#discussion_r1094576510
##########
docs/source/format/CanonicalExtensions.rst:
##########
@@ -72,4 +72,30 @@ same rules as laid out above, and provide backwards
compatibility guarantees.
Official List
=============
-No canonical extension types have been standardized yet.
+Fixed shape tensor
+==================
+
+* Extension name: `arrow.fixed_shape_tensor`.
+
+* The storage type of the extension: ``FixedSizeList`` where:
+
+ * **value_type** is the data type of individual tensors and
+ is an instance of ``pyarrow.DataType`` or ``pyarrow.Field``.
+ * **list_size** is the product of all the elements in tensor shape.
+
+* Extension type parameters:
+
+ * **value_type** = Arrow DataType of the tensor elements
+ * **shape** = shape of the contained tensors as a tuple
+
+* Description of the serialization:
+
+ The metadata must be a valid JSON object including shape of
+ the contained tensors as an array with key "shape".
+
+ For example: `{ "shape": [2, 5]}`
+
+.. note::
+
+ Elements in an fixed shape tensor extension array are stored
+ in row-major/C-contiguous order.
Review Comment:
On further thinking, I am also not sure this is actually a problem.
Languages like Julia and R can still create an array/matrix from the raw memory
of the ListArray zero-copy. This array will only look transposed to their users
if you need to prevent the copy. It's then up to the application/user to decide
if you want to keep that or not (have a strided view in expected dimension
order, or create a copy)?
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