colorbar with dates #17447

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1. jklymak commented on May 18, 2020

   

   jklymak

   on May 18, 2020

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   Can you reproduce a self contained example here?

   In general matplotlib does not do automatic conversion on the data that is run through a norm so expect to jump through some hoops to get a colorbar with dates on it.
2. c-foschi commented on May 19, 2020

   

   c-foschi

   on May 19, 2020

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   sure, here it is:

   import numpy as np
   import matplotlib.pyplot as plt
   
   dates = np.datetime64('2019-11') + np.arange(10)*np.timedelta64(1, 'D')
   X= np.random.randn(10, 2)
   
   plt.scatter(X[:, 0], X[:, 1], c= dates)
   plt.colorbar()
   plt.show()

   

   On the other hand, if I use the dates for some axis, they get printed just as dates:

   plt.scatter(X[:, 0], dates)
   plt.show()

   

   Well actually that scale could be improved, this is another problem, but fact is I think there is an inconsistency here between how dates are treated to make scales in axes, and to make scales on colorbars. Dates are not readable anymore when turned into numbers, and a scale is useless if not readable.
3. jklymak commented on May 19, 2020

   

   jklymak

   on May 19, 2020

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   The following is basically what is done for the x and y axis if the numpy array is a date. Adding the same support to the third dimension is really hard - in general, colormaps and colorbars are also used for images, pcolors, and contours, and the idea of those having convertible units is non-trivial.

   Here, you just convert the dates to floats and then set the proper formatters and locators:

   dates = np.datetime64('2019-11-01') + np.arange(10)*np.timedelta64(1, 'D')
   X= np.random.randn(10, 2)
   
   plt.scatter(X[:, 0], X[:, 1], c=mdates.date2num(dates))
   cb = plt.colorbar()
   loc = mdates.AutoDateLocator()
   cb.ax.yaxis.set_major_locator(loc)
   cb.ax.yaxis.set_major_formatter(mdates.ConciseDateFormatter(loc))
   plt.show()

   

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4. story645

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   topic: units and array ducktypes

   on May 19, 2020
5. story645 commented on May 19, 2020

   

   story645

   on May 19, 2020

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   and the idea of those having convertible units is non-trivial.

   Yes/No - I think you might be able to get it by putting a convertor on NoNorm.
6. jklymak commented on May 19, 2020

   

   jklymak

   on May 19, 2020

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   Its not the conversion thats particularly the issue, its getting the unit info down to the colorbar.
7. dstansby

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8. github-actions commented on Aug 2, 2023

   

   github-actionsBot

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   This issue has been marked "inactive" because it has been 365 days since the last comment. If this issue is still present in recent Matplotlib releases, or the feature request is still wanted, please leave a comment and this label will be removed. If there are no updates in another 30 days, this issue will be automatically closed, but you are free to re-open or create a new issue if needed. We value issue reports, and this procedure is meant to help us resurface and prioritize issues that have not been addressed yet, not make them disappear. Thanks for your help!
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