Repository navigation
[ENH]: scalermappable bar #26312
Description
Problem
Coloring the bars in the bar chart based on some value isn't uncommon (#23265, #26310) and colors=cmap(norm(values)) is serviceable but it'd be nice if folks could directly set the cmap, norm, and data separately-especially for legend and colorbar creation.
Proposed solution
While it has it's problems, scatter has an API for how to manage colormap/norm or colors for discrete markers, so I think it would stay consistent if the scatter API for colors could be ported to bars. Could then probably adapt scatter.legend_elements implementation to auto generate legends from the colors.
ETA: If we did this, it'd probably also be a good reason to implement #7383
Activity
anntzer commentedon Jul 15, 2023
While it is not strictly necessary, I think this would be conceptually related to moving bar() to return a single PathCollection (#22976), which is a fair bit of work but which I now think could be done in a way similar to the ContourSet transition recently merged (#25247).
timhoffm commentedon Jul 16, 2023
Gradient bars
Note that #23265 is asking for "draw 3d bars gradient", which is the second example in https://de.mathworks.com/help/matlab/creating_plots/color-3-d-bars-by-height-1.html.
Even with a scalarmappable bar, we'll not be able to support this. One could achive this with a value-scaled variation of https://matplotlib.org/stable/gallery/lines_bars_and_markers/gradient_bar.html#sphx-glr-gallery-lines-bars-and-markers-gradient-bar-py. But I think we're far from internal code structures or an API needed to include this as a builtin feature.
For now, I'd say, this are out of scope.
Color-coded bars
This is fundamentally reasonable, even though #26310 is not making a good case for it.
We have basically two cases:
1. discrete colors that show up in the legend.
Examples:
These are already handled via https://matplotlib.org/stable/gallery/lines_bars_and_markers/bar_colors.html
2. Continuous colors.
I've found two classes of examples:
Purely artistic ones
These do not need a legend and thus,
is enough. (Apart from the question whether one should do this at all).
Continous color coding:
e.g.
This needs a colorbar as reference and is the only case possibly warranting an extension of our API. Be aware though that bars have color, edgecolor and ecolor (errorbars). And that we need a conscious decision how to handle them (likely only provide colormapping for the face color).
rather replace
BarContainer.patches(currently list of Rectangle) by a collection. (t.b.d. wether a generalPathCollectionis suitable or whether a dedicatedRectangleCollectionis justified.