[GitHub] [arrow] paleolimbot commented on a diff in pull request #33925: GH-33923: [Docs] Tensor canonical extension type specification

["paleolimbot (via GitHub)" <gi...@apache.org>]

paleolimbot commented on code in PR #33925:
URL: https://github.com/apache/arrow/pull/33925#discussion_r1094551041


##########
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:
   Just a note that this will prevent storing R matrices as zero-copy. I seem to remember an earlier version of this had an option for storing column-major tensors zero-copy?



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