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ENH: LogLocator can auto-select number of ticks based on axis #7126

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Merged
merged 1 commit into from
Sep 19, 2016
Merged

ENH: LogLocator can auto-select number of ticks based on axis #7126

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Binary file added lib/matplotlib/tests/baseline_images/test_axes/auto_numticks_log.png
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10 changes: 10 additions & 0 deletions lib/matplotlib/tests/test_axes.py
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Original file line number Diff line number Diff line change
Expand Up @@ -4418,9 +4418,19 @@ def test_adjust_numtick_aspect():
@image_comparison(baseline_images=["auto_numticks"], style='default',
extensions=['png'])
def test_auto_numticks():
# Make tiny, empty subplots, verify that there are only 3 ticks.
fig, axes = plt.subplots(4, 4)


@image_comparison(baseline_images=["auto_numticks_log"], style='default',
extensions=['png'])
def test_auto_numticks_log():
# Verify that there are not too many ticks with a large log range.
fig, ax = plt.subplots()
matplotlib.rcParams['axes.autolimit_mode'] = 'round_numbers'
ax.loglog([1e-20, 1e5], [1e-16, 10])


@cleanup
def test_broken_barh_empty():
fig, ax = plt.subplots()
Expand Down
41 changes: 29 additions & 12 deletions lib/matplotlib/ticker.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1639,8 +1639,11 @@ def set_params(self, **kwargs):

def _raw_ticks(self, vmin, vmax):
if self._nbins == 'auto':
nbins = max(min(self.axis.get_tick_space(), 9),
max(1, self._min_n_ticks - 1))
if self.axis is not None:
nbins = max(min(self.axis.get_tick_space(), 9),
max(1, self._min_n_ticks - 1))
else:
nbins = 9
else:
nbins = self._nbins

Expand Down Expand Up @@ -1757,15 +1760,19 @@ class LogLocator(Locator):
Determine the tick locations for log axes
"""

def __init__(self, base=10.0, subs=(1.0,), numdecs=4, numticks=15):
def __init__(self, base=10.0, subs=(1.0,), numdecs=4, numticks=None):
"""
place ticks on the location= base**i*subs[j]
"""
if numticks is None:
if rcParams['_internal.classic_mode']:
numticks = 15
else:
numticks = 'auto'
self.base(base)
self.subs(subs)
# this needs to be validated > 1 with traitlets
self.numticks = numticks
self.numdecs = numdecs
self.numticks = numticks

def set_params(self, base=None, subs=None, numdecs=None, numticks=None):
"""Set parameters within this locator."""
Expand All @@ -1786,7 +1793,7 @@ def base(self, base):

def subs(self, subs):
"""
set the minor ticks the log scaling every base**i*subs[j]
set the minor ticks for the log scaling every base**i*subs[j]
"""
if subs is None:
self._subs = None # autosub
Expand All @@ -1799,6 +1806,14 @@ def __call__(self):
return self.tick_values(vmin, vmax)

def tick_values(self, vmin, vmax):
if self.numticks == 'auto':
if self.axis is not None:
numticks = max(min(self.axis.get_tick_space(), 9), 2)
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I understand the minimum of 2, but 9 seems a bit of a random number. Why was this chosen?

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You are right, it is pretty random. It is the default max we chose for the MaxNLocator auto algorithm, so I used it here as well. The rationale in both cases is that plots just don't look good with a huge number of major ticks; so 9 is random, but it "seems reasonable" as a limit. Nothing prevents a user from specifying a larger number instead of using the auto algorithm.

else:
numticks = 9
else:
numticks = self.numticks

b = self._base
# dummy axis has no axes attribute
if hasattr(self.axis, 'axes') and self.axis.axes.name == 'polar':
Expand Down Expand Up @@ -1836,12 +1851,14 @@ def tick_values(self, vmin, vmax):
subs = self._subs

stride = 1
if not self.numticks > 1:
raise RuntimeError('The number of ticks must be greater than 1 '
'for LogLocator.')
# FIXME: The following was designed for integer division in py2.
while numdec / stride + 1 > self.numticks:
stride += 1

if rcParams['_internal.classic_mode']:
# Leave the bug left over from the PY2-PY3 transition.
while numdec / stride + 1 > numticks:
stride += 1
else:
while numdec // stride + 1 > numticks:
stride += 1

decades = np.arange(math.floor(vmin) - stride,
math.ceil(vmax) + 2 * stride, stride)
Expand Down