[FEATURE REQUEST] append and vstack

[kwagyeman]

Describe the solution you'd like
I would like if append() and vstack() could be implemented.

Also if this limitation could be removed.

Indices can also be a list of Booleans. By using a Boolean list, we can select those elements of an array that satisfy a specific condition. At the moment, such indexing is defined for row vectors only; when the rank of the tensor is higher than 1, the function raises a NotImplementedError exception, though this will be rectified in a future version of ulab.

Additional context
I was trying to implement non-max-suppression using Ulab and ran into the lack of these features complicating things for me.

Happy to finance this work.

[v923z]

append should be relatively straightforward, and others might also find it useful, so I would be happy to add it.

Reading the documentation of vstack, it seems to me that it's only a shortcut to what you can already do: concatenate has already been implemented. If that doesn't match your requirements, we could discuss the addition of vstack.

Also if this limitation could be removed.

Do you mean the fact that Boolean indices are supposed to be 1D arrays, or something else?

[kwagyeman]

Reading the documentation of vstack, it seems to me that it's only a shortcut to what you can already do: concatenate has already been implemented. If that doesn't match your requirements, we could discuss the addition of vstack.

It's more about making it easier to use desktop code directly without having to modify it too much. vstack would just be a wrapper around concatenate.

Do you mean the fact that Boolean indices are supposed to be 1D arrays, or something else?

If I try to use a 1D array of booleans to select rows from a 2D array you get a crash right now. Not a Not implemented error.

np_boxes is a 2D array of (x, y, w, h, score, class).

filtered_boxes = np_boxes[np_boxes[:, 4] > 0.0]

The above crashes.

[v923z]

If I try to use a 1D array of booleans to select rows from a 2D array you get a crash right now. Not a Not implemented error.

np_boxes is a 2D array of (x, y, w, h, score, class).

filtered_boxes = np_boxes[np_boxes[:, 4] > 0.0]

The above crashes.

OK, this is a different issue then, thanks for bringing it up! I opened a ticket here #672, so that it can be addressed.

[kwagyeman]

@v923z - Any updates on this?

[v923z]

Merging the implementation of take would address the issue raised here, too, right?

[kwagyeman]

This is more of just a wrapper around concatenate so that append/vstack work. Would be great to have them as normal so desktop code just works.

Yes, otherwise, take addresses the other issue in the thread.

[v923z]

Wrappers should/could be added in https://github.com/v923z/micropython-ulab/tree/master/snippets. That has the advantage that that doesn't consume irrecoverable flash space.

[kwagyeman]

If it's controlled by an ifdef that works for me. It can be off by default and I can enable it for the OpenMV Cams.

[v923z]

Everything in https://github.com/v923z/micropython-ulab/tree/master/snippets is in the python layer, so you can simply decide, whether you ship the wrapper with your firmware.

[v923z]

Addressed by #688.