'levels' tick labels for discrete colormaps

[paulvija]

Hi there,

'levels' tick labels for discrete colormaps works fine for 10 intervals and tend to shorten by itself beyond 10. This behavior may exist to make colorbar exceeding 10 intervals look tidy.

However, for discrete colormaps it will be good to label the ticks for all intervals as they can be any number and not uniform.
xray.version = '0.8.2'

Please see the screenshots attached for a better understanding.

Thanks,
Vijay Paul

[shoyer]

Agreed, this would be nice. See also #920.

[fmaussion]

Note that currently the colorbar labelling logic is handed over entirely to matplotlib, so its mpl which decides upon this. With the cbar_kwargs argument you can control this at your whish, so I'm not sure we have to change anything:

from matplotlib import pyplot as plt
import xarray as xr

data = xr.DataArray(np.arange(12).reshape((3, 4))*10 + 10)
levels = np.append(np.arange(10)*10 + 10, 115)

f, (ax1, ax2, ax3) = plt.subplots(1, 3, figsize=(14, 4))

data.plot(ax=ax1, levels=levels)
data.plot(ax=ax2, levels=levels, cbar_kwargs={'ticks':levels})
data.plot(ax=ax3, levels=levels, cbar_kwargs={'ticks':levels, 'spacing':'proportional'})
plt.tight_layout()

[paulvija]

cbar_kwargs works well for my purpose (plot.pcolormesh). Thanks for the help.
Can this usage be shown in the documentation, at least mentioning that colorbar intervals can be placed at our wish or this comes under matplotlib?

[shoyer]

@paulvija @fmaussion either of you interested in putting together a PR? :)

[paulvija]

PR?

Date: Thu, 22 Sep 2016 18:50:52 -0700
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CC: vijay.paul@outlook.co.nz; mention@noreply.github.com
Subject: Re: [pydata/xarray] 'levels' tick labels for discrete colormaps (#1015)

@paulvija @fmaussion either of you interested in putting together a PR? :)

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[shoyer]

Sorry, PR is github short hand for "pull request". See
http://pandas.pydata.org/pandas-docs/stable/contributing.html for guidance.

On Thu, Sep 22, 2016 at 6:54 PM, Vijay Paul notifications@github.com
wrote:

PR?

Date: Thu, 22 Sep 2016 18:50:52 -0700
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To: xarray@noreply.github.com
CC: vijay.paul@outlook.co.nz; mention@noreply.github.com
Subject: Re: [pydata/xarray] 'levels' tick labels for discrete colormaps
(#1015)

@paulvija @fmaussion either of you interested in putting together a PR? :)

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[paulvija]

Got it! Thanks, I am keen to contribute with a short example.

[dcherian]

Should we set cbar_kwargs to contain {'ticks':levels, 'spacing':'proportional'} when levels is specified or only have this as a documentation fix?

[fmaussion]

I think a doc example would be enough. For example in the gallery? http://xarray.pydata.org/en/latest/auto_gallery/index.html