Violin plots crash when given all zeros

[slinnarsson]

I'm truly enjoying learning HoloViews - such a great visualization library!

I encountered a bug, I think. Changing the Violin plot example to give it all zeros causes an exception:

>>> groups = [chr(65+g) for g in np.random.randint(0, 3, 200)]
>>> hv.Violin((groups, np.random.randint(0, 5, 200), np.zeros(200)), ['Group', 'Category'], 'Value')
(...stack trace here...)
TypeError: 'NoneType' object is not iterable

Most likely the kernel density estimation fails. This is an issue for visualizing many groups, when one or more groups may be all zeros. The expected result is a flat line, I suppose (this is what BoxWhisker does).

[ea42gh]

hv.Violin([]) fails as well

[jlstevens]

Thanks @slinnarsson and @ea42gh! I agree both those issues are bugs.