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hist(): align!='mid' and unequally spaced bins don't play well together. #12524

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hist(): align!='mid' and unequally spaced bins don't play well together. #12524

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7 changes: 7 additions & 0 deletions lib/matplotlib/axes/_axes.py
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Original file line number Diff line number Diff line change
Expand Up @@ -6644,6 +6644,13 @@ def hist(self, x, bins=None, range=None, density=False, weights=None,
# so that each histogram uses the same bins
m, bins = np.histogram(x[i], bins, weights=w[i], **hist_kwargs)
tops.append(m)

# align != 'mid' only makes sense for equal-sized bins.
if align != 'mid' and not cbook._is_equally_spaced(bins):
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I think this should only apply to the step-like functions, so if histtype in ['step', 'stepfilled'] ...
For the bar-like functions, it may not make too much sense, but at least it's not wrong.

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I think #12494 shows very clearly that whoever implemented align did not take non-equally-spaced bins into account, and while the result is "not wrong", it doesn't make much sense either.

raise ValueError(
"When 'bins' are not equally spaced, the only valid value for "
"'align' is 'mid'")

tops = np.array(tops, float) # causes problems later if it's an int
if stacked:
tops = tops.cumsum(axis=0)
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7 changes: 7 additions & 0 deletions lib/matplotlib/cbook/__init__.py
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Expand Up @@ -2165,3 +2165,10 @@ def __init__(self, fget):

def __get__(self, instance, owner):
return self._fget(owner)


def _is_equally_spaced(x):
"""
Return whether the values in *x* are equally spaced (up to fp errors).
"""
return len(x) < 2 or np.allclose(np.diff(x), (x[-1] - x[0]) / (len(x) - 1))
4 changes: 2 additions & 2 deletions lib/matplotlib/streamplot.py
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Expand Up @@ -340,9 +340,9 @@ def __init__(self, x, y):
self.width = x[-1] - x[0]
self.height = y[-1] - y[0]

if not np.allclose(np.diff(x), self.width / (self.nx - 1)):
if not cbook._is_equally_spaced(x):
raise ValueError("'x' values must be equally spaced")
if not np.allclose(np.diff(y), self.height / (self.ny - 1)):
if not cbook._is_equally_spaced(y):
raise ValueError("'y' values must be equally spaced")

@property
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5 changes: 5 additions & 0 deletions lib/matplotlib/tests/test_axes.py
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Expand Up @@ -3278,6 +3278,11 @@ def test_hist_labels():
assert l[2][0].get_label() == '00'


def test_hist_invalid_combinations():
with pytest.raises(ValueError):
plt.figure().subplots().hist([], bins=[0, 1/4, 1], align="left")


@image_comparison(['transparent_markers'], remove_text=True)
def test_transparent_markers():
np.random.seed(0)
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