Arviz: Color scheme not displayed in plot_energy.

[Ban-zee]

The color scheme is not displayed in the legend for a default energy plot.

This behavior is not observed when we set kind='hist'.

[OriolAbril]

Good catch! I checked the code a little, and this is a problem of plot_kde. The label is set in ax.plot, therefore, when alpha=0 (or linewidth=0) in plot_kwargs the legend is empty. Here is another example:

>>> az.plot_kde(np.random.normal(size=1000), label="Gaussian", plot_kwargs={"alpha":0}, fill_kwargs={"alpha":.7}) 
# equivalent to
# az.plot_kde(np.random.normal(size=1000), label="Gaussian", plot_kwargs={"linewidth":0}, fill_kwargs={"alpha":.7})

Outputs:

This can be solved creating the legend from handles. The only thong that will be a little tricky will be passing the arguments in plot_kwargs and fill_kwargs to the matplotlib Patch. I have plenty of experience with this kind of legends, I can try to solve it or help anyone who volunteers. It can also be useful to avoid the ghost plots in plot_energy when bfmi=True.

[Ban-zee]

In this case, I'll start working on the issue and you can help me in the process.

[OriolAbril]

Great! Feel free to ask anything via gitter. I will also send you some reference that may be useful. I have one starting comment though, which is interesting for everyone too. The docs say _use fill_kwargs={‘alpha’: 0} to disable fill_. And the same approach is used in plot_energy to disable the line plot. However, I think it may be a better idea to use linewidth=0 to disable line plots, which will also make it easier when generating the custom legend handles.

[Ban-zee]

Amazing. I'll start work on this soon.

[ahartikainen]

Do we really need the patch here? Could we just pop the label kw out from plot_kwargs and add it to fill_kwargs iff lw=0? Then maybe remove its alpha? Or atleast make sure it is not close to 0?

[OriolAbril]

This is also an option, however the results when both line and fill are present could be weird. I am not sure if this would actually be less work to the patch in plot_kde. However, this approach will probably make solving the problems in plot_energy easier.

[Ban-zee]

Issue's been resolved. I'll close it now.