[jira] [Created] (ARROW-5857) [Python] converting multidimensional numpy arrays to nested list type

["Joris Van den Bossche (JIRA)" <ji...@apache.org>]

Joris Van den Bossche created ARROW-5857:
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             Summary: [Python] converting multidimensional numpy arrays to nested list type
                 Key: ARROW-5857
                 URL: https://issues.apache.org/jira/browse/ARROW-5857
             Project: Apache Arrow
          Issue Type: Improvement
          Components: Python
            Reporter: Joris Van den Bossche


Currently we only support 1-dimensional numpy arrays:

{code:python}
In [28]: pa.array([np.array([[1, 2], [3, 4]])], type=pa.list_(pa.list_(pa.int64()))) 
...
ArrowInvalid: Can only convert 1-dimensional array values
{code}

So to create a nested list array, you can do that with lists of lists or object numpy arrays with arrays as elements. We could expand this support to multi-dimensional numpy arrays.

I am not sure we should do inference by default for this case, but at least when specifying a nested ListType, this would be nice. 

It can be an alternative way to have some support for tensors, next to an ExtensionType (ARROW-1614 / ARROW-5819)

Related discussions: https://lists.apache.org/thread.html/9b142c1709aa37dc35f1ce8db4e1ced94fcc4cdd96cc72b5772b373b@%3Cdev.arrow.apache.org%3E, https://github.com/apache/arrow/issues/4802



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