Add dimension slicer plot

[nvaytet]

This allows to slice higher dimensions with sliders.

Example:

%matplotlib widget
import plopp as pp

da = pp.data.dense_data_array(ndim=3)
pp.slicer(da, keep=['z', 'y'])  # slice out dimension 'x' -> makes a 2d image with 1 slider
pp.slicer(da, keep=['z'])  # slice out dimensions 'x' and 'y' -> makes a 1d line with 2 sliders

We are not adding the buttons from the old plotting that allowed to flip the dimensions interactively because this would lead to too much entangled code between the Mesh and the Figure, where a new Mesh would have to be made, the axis limits would have to be changed, and what to do with the log scales of the axes.

Instead, we make an easy to use API where keep is a list of dimensions to allow the user to quickly get what they want by re-plotting, instead of changing dims dynamically after the plot was made.

Fixes #14

[SimonHeybrock]

pp.slicer(da, dims=['x'])  # slice out dimension 'x' -> makes a 2d image with 1 slider
pp.slicer(da, dims=['x', 'y'])  # slice out dimensions 'x' and 'y' -> makes a 1d line with 2 sliders

Comment before having looked at the implementation: I feel this is backwards. Wouldn't it be more natural to specify the dims the user wants to see?

[SimonHeybrock]

We are not adding the buttons from the old plotting that allowed to flip the dimensions interactively because this would lead to too much entangled code between the Mesh and the Figure, where a new Mesh would have to be made, the axis limits would have to be changed, and what to do with the log scales of the axes.

Would it be an option to make one plot for each axis combination, and show only the selected one? The old buttons next to the slider essentially act like tab-selection buttons, i.e., it simply selects a different figure to show.

[nvaytet]

Comment before having looked at the implementation: I feel this is backwards. Wouldn't it be more natural to specify the dims the user wants to see?

I don't mind either way.
Maybe we should call the argument keep like in sc.collapse?

pp.slicer(da, keep=['x'])  # keep only 'x' -> makes a 1d line with 2 sliders
pp.slicer(da, keep=['x', 'y'])  # keep 'x' and 'y' -> makes a 2d image with 1 slider along 'z'

[nvaytet]

Would it be an option to make one plot for each axis combination, and show only the selected one? The old buttons next to the slider essentially act like tab-selection buttons, i.e., it simply selects a different figure to show.

I feel this is really adding complication for not much gain. And the different tabs wouldn't help you with the handling of the log scales on the axes.
I really don't think the buttons will be used much, if it's easy for the user to specify when making the plot what they want to keep/slice.

In any case, I don't want to add them now and make things more complicated than they are. If users later say this is an absolute must have, then we can add them later, maybe using what you suggest.

[SimonHeybrock]

Comment before having looked at the implementation: I feel this is backwards. Wouldn't it be more natural to specify the dims the user wants to see?

I don't mind either way. Maybe we should call the argument keep like in sc.collapse?

pp.slicer(da, keep=['x'])  # keep only 'x' -> makes a 1d line with 2 sliders
pp.slicer(da, keep=['x', 'y'])  # keep 'x' and 'y' -> makes a 2d image with 1 slider along 'z'

We should probably just get user feedback/opinions.

[SimonHeybrock]

As shown by a user comment on Slack, the name "Slicer" may be misleading?

[nvaytet]

Any better ideas?

[SimonHeybrock]

Ask the users?

[nvaytet]

Greg says slicer is fine in the end.

[SimonHeybrock]

Really?

[nvaytet]

I don't know how to make this specific to Matplotlib. This arose when updating to Matplotlib 3.6 where get_cmap raises this warning. They say to use the syntax

cmap = matplotlib.colormaps[name]

instead of

cmap = matplotlib.cm.get_cmap(name)

However, the new syntax does not exist in mpl<3.5. I thought I would keep it compatible?
Alternatively I can just use the new syntax and put a lower bound on the MPL requirement?
What do you think?

[SimonHeybrock]

Leave it for now.

[SimonHeybrock]

Type hints should take care of this?

[nvaytet]

Merging so I can more easily move with other PRs