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Gracefully handle 0s when plotting in log scale #563

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Gracefully handle 0s when plotting in log scale #563

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b176152
Gracefully handle 0s when plotting in log scale
JamesWrigley Jul 20, 2022
23b8acf
fixup! Gracefully handle 0s when plotting in log scale
JamesWrigley Jul 21, 2022
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5 changes: 3 additions & 2 deletions extra_foam/gui/plot_widgets/tests/test_plot_items.py
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Original file line number Diff line number Diff line change
Expand Up @@ -92,15 +92,16 @@ def testCurvePlotItem(self, dtype):
item.setData(np.arange(2).astype(dtype), np.arange(3).astype(dtype))

# test log mode
plot_bottom_right = np.log10(float(x[-1]))
self._widget._plot_area._onLogXChanged(True)
if dtype == float:
_display()
assert item.boundingRect() == QRectF(0, 0, 1.0, 13.5)
assert item.boundingRect() == QRectF(0, 0, plot_bottom_right, 13.5)
self._widget._plot_area._onLogYChanged(True)
if dtype == float:
_display()
assert item.boundingRect().topLeft() == QPointF(0, 0)
assert item.boundingRect().bottomRight().x() == 1.0
assert item.boundingRect().bottomRight().x() == plot_bottom_right
assert 1.2 > item.boundingRect().bottomRight().y() > 1.1

# clear data
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2 changes: 1 addition & 1 deletion extra_foam/gui/pyqtgraph/graphicsItems/GraphicsObject.py
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Original file line number Diff line number Diff line change
Expand Up @@ -129,7 +129,7 @@ def toLogScale(arr, policy=None):
"""Convert array result to logarithmic scale."""
ret = np.nan_to_num(arr)
ret[ret < 0] = 0
return np.log10(ret + 1)
return np.log10(ret, where=(ret > 0))
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I agree that the original solution does not work in some situations, as you have shown. However, there are also corner cases for the new one. It makes 1 and 0 the same. 0 will not be affected while 1 will become 0 after the log operation. Imaging you have a step function f(x) = 1 if x > 0 else 0, with the new solution the curve will become completely flat (all 0). Therefore, a better solution might be letting users choose among different methods.


def name(self):
"""An identity of the PlotItem.
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