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Avoid 1-tick or 0-tick log-scaled axis. #12865

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Merged
merged 1 commit into from
Nov 28, 2018
Merged

Avoid 1-tick or 0-tick log-scaled axis. #12865

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6 changes: 6 additions & 0 deletions doc/api/next_api_changes/2018-11-23-AL.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,6 @@
Log-scaled axes avoid having zero or only one tick
``````````````````````````````````````````````````

When the default `LogLocator` would generate no ticks for an axis (e.g., an
axis with limits from 0.31 to 0.39) or only a single tick, it now instead falls
back on the linear `AutoLocator` to pick reasonable tick positions.
7 changes: 6 additions & 1 deletion lib/matplotlib/tests/test_ticker.py
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@@ -1,7 +1,7 @@
import warnings

import numpy as np
from numpy.testing import assert_almost_equal
from numpy.testing import assert_almost_equal, assert_array_equal
import pytest

import matplotlib
Expand Down Expand Up @@ -179,6 +179,11 @@ def test_basic(self):
test_value = np.array([0.5, 1., 2., 4., 8., 16., 32., 64., 128., 256.])
assert_almost_equal(loc.tick_values(1, 100), test_value)

def test_switch_to_autolocator(self):
loc = mticker.LogLocator(subs="all")
assert_array_equal(loc.tick_values(0.45, 0.55),
[0.44, 0.46, 0.48, 0.5, 0.52, 0.54, 0.56])

def test_set_params(self):
"""
Create log locator with default value, base=10.0, subs=[1.0],
Expand Down
34 changes: 21 additions & 13 deletions lib/matplotlib/ticker.py
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Expand Up @@ -2165,13 +2165,13 @@ def tick_values(self, vmin, vmax):
"log-scaled.")

_log.debug('vmin %s vmax %s', vmin, vmax)
vmin = math.log(vmin) / math.log(b)
vmax = math.log(vmax) / math.log(b)

if vmax < vmin:
vmin, vmax = vmax, vmin
log_vmin = math.log(vmin) / math.log(b)
log_vmax = math.log(vmax) / math.log(b)

numdec = math.floor(vmax) - math.ceil(vmin)
numdec = math.floor(log_vmax) - math.ceil(log_vmin)

if isinstance(self._subs, str):
_first = 2.0 if self._subs == 'auto' else 1.0
Expand All @@ -2195,32 +2195,40 @@ def tick_values(self, vmin, vmax):
while numdec // stride + 1 > numticks:
stride += 1

# Does subs include anything other than 1?
# Does subs include anything other than 1? Essentially a hack to know
# whether we're a major or a minor locator.
have_subs = len(subs) > 1 or (len(subs) == 1 and subs[0] != 1.0)

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

if hasattr(self, '_transform'):
ticklocs = self._transform.inverted().transform(decades)
if have_subs:
if stride == 1:
ticklocs = np.ravel(np.outer(subs, ticklocs))
else:
# no ticklocs if we have more than one decade
# between major ticks.
ticklocs = []
# No ticklocs if we have >1 decade between major ticks.
ticklocs = np.array([])
else:
if have_subs:
ticklocs = []
if stride == 1:
for decadeStart in b ** decades:
ticklocs.extend(subs * decadeStart)
ticklocs = np.concatenate(
[subs * decade_start for decade_start in b ** decades])
else:
ticklocs = np.array([])
else:
ticklocs = b ** decades

_log.debug('ticklocs %r', ticklocs)
return self.raise_if_exceeds(np.asarray(ticklocs))
if (len(subs) > 1
and stride == 1
and ((vmin <= ticklocs) & (ticklocs <= vmax)).sum() <= 1):
# If we're a minor locator *that expects at least two ticks per
# decade* and the major locator stride is 1 and there's no more
# than one minor tick, switch to AutoLocator.
return AutoLocator().tick_values(vmin, vmax)
return self.raise_if_exceeds(ticklocs)

def view_limits(self, vmin, vmax):
'Try to choose the view limits intelligently'
Expand Down