[AstroPy] matplotlib histograms and astropy quantites

[Daniel Evans]

John,

My version of astropy is far too ancient to have this feature (I should bug
my sysadmin!) so I can't test it myself, but does calling
astropy.visualization.quantity_support() fix your errors?

"Enable support for plotting astropy.units.Quantity instances in
matplotlib."
http://docs.astropy.org/en/stable/api/astropy.visualization.quantity_support.html#astropy.visualization.quantity_support

Regards,
Daniel

On 27 July 2016 at 10:00, John K. Parejko <parejkoj at uw.edu> wrote:

> I wonder if I'm misusing astropy quantities, or if there's a bug with how
> it interacts with matplotlib's pyplot.hist (and thus np.histogram). I've
> attached a minimal working example that represents a histogram I was
> attempting to create. If you try to make the plot range be a unit, plt.hist
> will fail. I would have thought that I could specify a range with units and
> get the plot axis to match the units I want to show the data with.
>
> Also, trying to draw a vertical line with axvline() on a Quantity fails,
> though I guess I shouldn't be surprised at that. But given the above, this
> was also surprising to me.
>
> I feel like there could be some more documentation about the interaction
> between astropy quantities and matplotlib?
>
> Am I missing something here?
>
> Thanks in advance,
> John
>
>
> import numpy as np
> from astropy import units as u
> import matplotlib.pyplot as plt
>
> range1 = (-3, 3)
> range2 = range1*u.arcsecond
> np.random.seed(100)
> data = np.random.normal(scale=3e-6, size=100)*u.radian
> plt.figure()
> # Not well centered and wrong X scale.
> plt.hist(data)
> # Works: I guess I shouldn't be surprised that I have to extract a value
> here.
> plt.axvline(x=data[0].value, color='red')
> plt.figure()
> # Wanted the range in arcseconds, so this isn't right!
> plt.hist(data, range=range1)
> # Dimensionalizing it seems to work correctly.
> plt.axvline(x=data[0]/u.arcsecond, color='red')
> plt.figure()
> # UnitsError: Can only apply 'less_equal' function to dimensionless
> quantities...
> plt.hist(data, range=range2)
> # UnitsError: Can only apply 'greater' function to dimensionless
> quantities...
> plt.axvline(x=data[0])
>
>
>
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