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FIX: be more careful about coercing unit-full containers to ndarray #21884

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Dec 10, 2021
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FIX: be more careful about coercing unit-full containers to ndarray #21884

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FIX: be more careful about coercing unit-full containers to ndarray
tacaswell Dec 8, 2021
d52c2e8
FIX: be even more careful about handling yerr/yerr input
tacaswell Dec 9, 2021
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50 changes: 48 additions & 2 deletions lib/matplotlib/axes/_axes.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3282,10 +3282,56 @@ def errorbar(self, x, y, yerr=None, xerr=None,
x = np.asarray(x, dtype=object)
if not isinstance(y, np.ndarray):
y = np.asarray(y, dtype=object)

def _upcast_err(err):
"""
Safely handle tuple of containers that carry units.

If the units are carried on the values then casting to object
arrays preserves the units, but if the units are on the containers
this will not work.
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I find the docstring confusing, mixing the what and the why in a way that I can't sort out.
I suggest simply stating what it does under each case it handles.


This function covers the case where the input to the xerr/yerr is a
length 2 tuple of equal length ndarray-subclasses that carry the
unit information in the container.

We defer coercing the units to be consistent to the underlying unit
library (and implicitly the broadcasting).

If we do not have a tuple of nested numpy array (subclasses),
fallback to casting to an object array.

"""

# we are here because we the container is not a numpy array, but it
# _is_ iterable (likely a list or a tuple but maybe something more
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But at this point you don't know it is iterable--you check it. If it is not iterable, you still wrap it in an object array.

# exotic)

if (
# make sure it is not a scalar
np.iterable(err) and
# and it is not empty
len(err) > 0 and
# and the first element is an array sub-class use
# safe_first_element because getitem is index-first not
# location first on pandas objects so err[0] almost always
# fails.
isinstance(cbook.safe_first_element(err), np.ndarray)
):
# grab the type of the first element, we will try to promote
# the outer container to match the inner container
atype = type(cbook.safe_first_element(err))
# you can not directly pass data to the init of `np.ndarray`
if atype is np.ndarray:
return np.asarray(err, dtype=object)
# but you can for unyt and astropy uints
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astropy "units", I presume

return atype(err)
return np.asarray(err, dtype=object)

if xerr is not None and not isinstance(xerr, np.ndarray):
xerr = np.asarray(xerr, dtype=object)
xerr = _upcast_err(xerr)
if yerr is not None and not isinstance(yerr, np.ndarray):
yerr = np.asarray(yerr, dtype=object)
yerr = _upcast_err(yerr)
x, y = np.atleast_1d(x, y) # Make sure all the args are iterable.
if len(x) != len(y):
raise ValueError("'x' and 'y' must have the same size")
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