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[ENH]: contour kwarg for negative_linestyle #23028
Description
Problem
if you contour a negative quantity, it gets dashed lines. Leaving aside whether this is a good default or not, the only way to toggle this is via rcParams['contour.negative_linestyle']=False.
Proposed solution
I think this should be togglable via kwarg, though I appreciate that overlaps with linestyle and only is activated with monochrome contours.
(I actually think the default should be False, FWIW - this surprises me every time, and I make quite a few contour plots).
Activity
andrew-fennell commented on May 13, 2022
Should the current linestyles kwarg be used to accomplish this or should a new kwarg be added? I have a simple solution adding a new kwarg (though it would need a little more work before it is ready).
The following code snippet and images will show a solution with an added kwarg, but I expect this is not exactly what you had in mind.
import numpy as np import matplotlib.pyplot as plt delta = 0.025 x = np.arange(-3.0, 3.0, delta) y = np.arange(-2.0, 2.0, delta) X, Y = np.meshgrid(x, y) Z1 = np.exp(-X**2 - Y**2) Z2 = np.exp(-(X - 1)**2 - (Y - 1)**2) Z = (Z1 - Z2) * 2 # Negative contour defaults to dashed fig, ax = plt.subplots() CS = ax.contour(X, Y, Z, 6, colors='k') ax.clabel(CS, fontsize=9, inline=True) ax.set_title('Single color - negative contours dashed (default)') # Set negative contours to be solid instead of dashed (default) # using negative_linestyle='solid' fig2, ax2 = plt.subplots() CS = ax2.contour(X, Y, Z, 6, colors='k', negative_linestyles='solid') ax2.clabel(CS, fontsize=9, inline=True) ax2.set_title('Single color - negative contours solid')Default
negative_linestyles='solid'
timhoffm commented on May 13, 2022
How would we squeeze this into the current linestyles parameter? The only thing I could imagine is something like linestyles={'positive': 'solid', 'negative': 'dotted'}, which I find a bit cumbersome. I suppose an extra kwarg is simpler.
andrew-fennell commented on May 13, 2022
I had no good solution for this either, but thought I would ask just in case.
The next question is:
I think the latter makes a lot more sense, but I don't work with contour plots regularly.
jklymak commented on May 13, 2022
I think since the rcParam is separate, its fine to keep the (potential) kwarg separate. BTW I'm not wedded to this idea, but it does seem strange to have a feature only accessible by rcParam.
As for bool vs string, I'd say both? right now the rcParam defaults to "dashed" - I think that's fine for a kwarg as well, but being able to say False to skip the behaviour would be nice as well.
andrew-fennell commented on May 13, 2022
I can mock-up a basic solution. Maybe we can get opinions from other contributors and maintainers in the meantime.
I think this would add value because it would make customization of negative contours more straightforward. Since this doesn't require removing any current functionality, I don't see any cons to adding the kwarg.