axhline/axvline broken with pint.Quantity #8910

dopplershift · 2017-07-18T22:25:52Z

With matplotlib 2.0.2, you can't use pint.Quantity with axhline or axvline:

%matplotlib inline

import matplotlib.pyplot as plt
import pint

units = pint.UnitRegistry()
fig, axes = plt.subplots(1, 1)
axes.axhline(0 * units.meter)

yields:

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-3-b77d6298b805> in <module>()
      6 units = pint.UnitRegistry()
      7 fig, axes = plt.subplots(1, 1)
----> 8 axes.axhline(0 * units.meter)

~/miniconda3/envs/py36/lib/python3.6/site-packages/matplotlib/axes/_axes.py in axhline(self, y, xmin, xmax, **kwargs)
    720         self._process_unit_info(ydata=y, kwargs=kwargs)
    721         yy = self.convert_yunits(y)
--> 722         scaley = (yy < ymin) or (yy > ymax)
    723 
    724         trans = self.get_yaxis_transform(which='grid')

~/miniconda3/envs/py36/lib/python3.6/site-packages/pint/quantity.py in <lambda>(self, other)
   1075                   other.to_root_units().magnitude)
   1076 
-> 1077     __lt__ = lambda self, other: self.compare(other, op=operator.lt)
   1078     __le__ = lambda self, other: self.compare(other, op=operator.le)
   1079     __ge__ = lambda self, other: self.compare(other, op=operator.ge)

~/miniconda3/envs/py36/lib/python3.6/site-packages/pint/quantity.py in compare(self, other, op)
   1065                 return op(self._convert_magnitude_not_inplace(UnitsContainer()), other)
   1066             else:
-> 1067                 raise ValueError('Cannot compare Quantity and {0}'.format(type(other)))
   1068 
   1069         if self._units == other._units:

ValueError: Cannot compare Quantity and <class 'numpy.float64'>

The text was updated successfully, but these errors were encountered:

dstansby · 2017-07-31T14:44:50Z

Looks like this is because there's not a suitible converter stored in the Matplotlib unit registry:

import matplotlib.pyplot as plt
import matplotlib.units as munits
import pint

units = pint.UnitRegistry()
for unit in munits.registry:
    print(unit)

prints

<class 'str'>
<class 'numpy.str_'>
<class 'bytes'>
<class 'numpy.bytes_'>
<class 'datetime.date'>
<class 'datetime.datetime'>

dopplershift · 2017-07-31T18:27:15Z

Quantity can quack like an array, so it should just pass through fine--like it does with plot
I've tried using the converters for this as well; any converter that doesn't just drop units fails as well.

I don't have an example for the second one above handy at the moment.

dstansby · 2017-08-08T16:35:57Z

Hmm, I can't get those units to work with plot:

import matplotlib.pyplot as plt
import pint

units = pint.UnitRegistry()
fig, ax = plt.subplots()
ax.plot([0 * units.meter, 1 * units.meter], [0 * units.meter, 1 * units.meter])
# ax.axhline(0 * units.meter)
plt.show()

fails with

Traceback (most recent call last):
  File "test.py", line 6, in <module>
    ax.plot([0 * units.meter, 1 * units.meter], [0 * units.meter, 1 * units.meter])
  File "/Users/dstansby/matplotlib/lib/matplotlib/__init__.py", line 1754, in inner
    return func(ax, *args, **kwargs)
  File "/Users/dstansby/matplotlib/lib/matplotlib/axes/_axes.py", line 1435, in plot
    for line in self._get_lines(*args, **kwargs):
  File "/Users/dstansby/matplotlib/lib/matplotlib/axes/_base.py", line 404, in _grab_next_args
    for seg in self._plot_args(this, kwargs):
  File "/Users/dstansby/matplotlib/lib/matplotlib/axes/_base.py", line 379, in _plot_args
    x = _check_1d(tup[0])
  File "/Users/dstansby/matplotlib/lib/matplotlib/cbook/__init__.py", line 1972, in _check_1d
    return np.atleast_1d(x)
  File "/Users/dstansby/miniconda3/lib/python3.6/site-packages/numpy/core/shape_base.py", line 52, in atleast_1d
    ary = asanyarray(ary)
  File "/Users/dstansby/miniconda3/lib/python3.6/site-packages/numpy/core/numeric.py", line 583, in asanyarray
    return array(a, dtype, copy=False, order=order, subok=True)
ValueError: setting an array element with a sequence.

dstansby · 2017-08-08T16:43:26Z

Quantity is not a subclass of ndarray. This might change in the future, but for this reason functions that call numpy.asanyarray are currently not supported
(from https://pint.readthedocs.io/en/0.7.2/numpy.html#support)

So it seems like calls to atleast_1d in our codebase means that pint.Units won't work?

dopplershift · 2017-08-08T17:02:58Z

You can't use pint that way. You need to do:

import matplotlib.pyplot as plt
import pint

units = pint.UnitRegistry()
fig, ax = plt.subplots()
ax.plot([0 , 1] * units.meter, [0, 1] * units.meter)
# ax.axhline(0 * units.meter)
plt.show()

That works fine for me.

Regarding atleast_1d, that's correct, they completely annihilate anything that's not a subclass of ndarray.

dopplershift · 2017-08-08T17:06:33Z

See #4803 where I "fixed" the use of atleast_1d for plot.

dopplershift · 2017-08-17T23:17:36Z

Well, it seems that things are better than I last checked when implementing a proper converter, at least with master:

from matplotlib.cbook import iterable
import matplotlib.pyplot as plt
import matplotlib.units as munits
import numpy as np
import pint

units = pint.UnitRegistry()


class PintConverter(munits.ConversionInterface):
    @staticmethod
    def convert(value, unit, axis):
        if hasattr(value, 'units'):
            return value.to(unit).magnitude
        elif iterable(value):
            try:
                return [v.to(unit).magnitude for v in value]
            except AttributeError:
                return [units.Quantity(v, axis.get_units()).to(unit).magnitude for v in value]
        else:
            return units.Quantity(value, axis.get_units()).to(unit).magnitude

    @staticmethod
    def default_units(x, axis):
        try:
            return x.units
        except AttributeError:
            return None

    @staticmethod
    def axisinfo(unit, axis):
        return munits.AxisInfo(label=unit)


# Register the class
munits.registry[units.Quantity] = PintConverter()

y = np.linspace(0, 30) * units.miles
x = np.linspace(0, 5) * units.hours

fig, ax = plt.subplots()
ax.plot(x, y, 'tab:blue')
ax.axhline((5 * units.miles).to('feet'), color='tab:red')
ax.axvline(120 * units.minutes, color='tab:green')
ax.yaxis.set_units(units.inches)
ax.xaxis.set_units(units.seconds)

Produces:

Once you add ax.autoscale_view() you get:

Which is actually correct. Now the question is why the autoscale doesn't kick off.

dopplershift · 2017-08-17T23:44:53Z

So it looks like only relim() is called when units change, which only refreshes the data limits, not the view limits.

I'm of the opinion we should also be calling autoscale_view when units change, what do others think?

dopplershift · 2017-08-17T23:47:58Z

As a side note, even if this "bug" only produces the smallest change here, I am so putting in a new test to make sure the current, desired behavior is preserved.

This tests that unit libraries that wrap arrays, like pint, work properly. This adds an image test that checks current behavior, which seems to be fully correct.

WeatherGod · 2017-08-21T20:26:44Z

perhaps relim() should be triggering an autoscale_view()?

…

On Thu, Aug 17, 2017 at 7:48 PM, Ryan May ***@***.***> wrote: As a side note, even if this "bug" only produces the smallest change here, I am *so* putting in a new test to make sure the current, desired behavior is preserved. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#8910 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AARy-Hl_4dq5xceIuWHNEk4p78Y3bHDRks5sZNEwgaJpZM4OcAEK> .

dopplershift · 2017-08-22T18:54:48Z

I sense those were de-coupled for performance reasons. We could add a callback to Axes (say, _on_units_changed) that calls both relim() and autoscale_view(), replacing the existing direct connection to relim`. Thoughts?

This tests that unit libraries that wrap arrays, like pint, work properly. This adds an image test that checks current behavior, which seems to be fully correct.

dopplershift · 2017-08-29T18:25:14Z

Fixed with #9049.

dopplershift added the topic: units and array ducktypes label Jul 18, 2017

dopplershift added this to the 2.1 (next point release) milestone Jul 18, 2017

dopplershift mentioned this issue Aug 18, 2017

BUG: Fix weird behavior with mask and units (Fixes #8908) #9049

Merged

dopplershift closed this as completed Aug 29, 2017

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axhline/axvline broken with pint.Quantity #8910

axhline/axvline broken with pint.Quantity #8910

dopplershift commented Jul 18, 2017

dstansby commented Jul 31, 2017

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dopplershift commented Aug 22, 2017

dopplershift commented Aug 29, 2017

axhline/axvline broken with pint.Quantity #8910

axhline/axvline broken with pint.Quantity #8910

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