Diverging Colorbar around Asymetric Data

HoloViews
#1

Hello,

is it possible to shift the “zero” point of a colorbar somehow? Say I have data from -8 to +2, and want the white to still be at 0:

import holoviews as hv
import numpy as np
import xarray as xr 
import hvplot.xarray

hv.extension('bokeh')
data = np.random.random((10,10))
data = 10 * (data - 0.8)
test_array = xr.DataArray(
    data,
    coords=[np.arange(10), np.arange(10)],
    dims=['x','y'], name='z')
test_array.hvplot(clim=(-8, 2), cmap="coolwarm")

This results in a figure, but obviously many of the negative values will still be red!

Screenshot 2022-02-03 at 16.08.10
Screenshot 2022-02-03 at 16.08.101002×494 15.8 KB

I found this, but cannot figure out how to use it:

There is:

bokeh.palettes.diverging_palette?

But this takes two colorbars, instead of 1.

#2

Here is one way to do it, but I don’t like it terribly. I am not sure if a) it covers all the colorbars available in holoviews (matplotlib, bokeh, colorcet, cmocean) and b) it would be nice to have an option to set in the hvplot or holoviews opts command

from matplotlib import colors
import numpy as np
divnorm = colors.TwoSlopeNorm(vmin=-8., vcenter=0., vmax=2)
levels = np.arange(-8, 2.5, 0.5)
colors = [colors.to_hex(c, keep_alpha=True) for c in plt.cm.coolwarm(divnorm(levels))]
test_array.hvplot(clim=(-8, 2), cmap=colors)
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