assign_subclass and signal with one value?

[magnunor]

In #2703, one of the tests is failing due to how s._assign_subclass works.

Essentially, should a signal with one value be a BaseSignal, or a Signal1D? Currently, _assign_subclass turns a signal with one value into a Signal1D, but the test expects it to be a BaseSignal.

To replicate this:

s = hs.signals.BaseSignal(1) # <BaseSignal, title: , dimensions: (|1)>
s._assign_subclass() # <Signal1D, title: , dimensions: (|1)>

The question is then which signal type should a signal with one value be? BaseSignal or Signal1D?

[jlaehne]

I would have thought that BaseSignal is just a parent class for all other signal classes, but is normally not used. Signal1D provides many additional routines, but then most of them don't make sense on a signal with one value only. So it seems to me to indeed be an edge case.

[thomasaarholt]

If the array is a zero-dimensional array, then I'd say it should probably go to basesignal or a "Signal0D".

[francisco-dlp]

HyperSpy does not support array scalars (i.e. 0-dimensional arrays) because scalar arrays, unlike ndarrays, are immutable. That's why HyperSpy converts any array scalar in a 1D array of shape [1].

This is indeed a corner case. Considering that, as pointed out by @jlaehne, most Signal1D methods make no sense for 1-element arrays, I think that it'll be better to assign them to BaseSignal.

[ericpre]

Done in #2773.