[RFC][ENH] OWScatterPlot: axis displays time specific labels for time variable

Orange/widgets/visualize/owscatterplot.py

@@ -119,6 +119,8 @@ def update_colors(self):
 
     def update_axes(self):
         for axis, title in self.master.get_axes().items():
+            use_time = title is not None and title.is_time
+            self.plot_widget.plotItem.getAxis(axis).use_time(use_time)
             self.plot_widget.setLabel(axis=axis, text=title or "")
             if title is None:
                 self.plot_widget.hideAxis(axis)

Orange/widgets/visualize/owscatterplotgraph.py

@@ -3,6 +3,8 @@
 import warnings
 from xml.sax.saxutils import escape
 from math import log10, floor, ceil
+from datetime import datetime, timezone
+from time import gmtime
 
 import numpy as np
 from AnyQt.QtCore import Qt, QRectF, QSize, QTimer, pyqtSignal as Signal, \
@@ -22,6 +24,7 @@
 )
 from pyqtgraph.graphicsItems.TextItem import TextItem
 
+from Orange.preprocess.discretize import _time_binnings
 from Orange.widgets.utils import colorpalettes
 from Orange.util import OrangeDeprecationWarning
 from Orange.widgets import gui
@@ -286,6 +289,77 @@ def _make_pen(color, width):
     return p
 
 
+class AxisItem(pg.AxisItem):
+    """
+    Axis that if needed displays ticks appropriate for time data.
+    """
+
+    _label_width = 80
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self._use_time = False
+
+    def use_time(self, enable):
+        """Enables axes to display ticks for time data."""
+        self._use_time = enable
+        self.enableAutoSIPrefix(not enable)
+
+    def tickValues(self, minVal, maxVal, size):
+        """Find appropriate tick locations."""
+        if not self._use_time:
+            return super().tickValues(minVal, maxVal, size)
+
+        # if timezone is not set, then local is used which cause exceptions
+        minVal = max(minVal,
+                     datetime.min.replace(tzinfo=timezone.utc).timestamp() + 1)
+        maxVal = min(maxVal,
+                     datetime.max.replace(tzinfo=timezone.utc).timestamp() - 1)
+        mn, mx = gmtime(minVal), gmtime(maxVal)
+
+        try:
+            bins = _time_binnings(mn, mx, 6, 30)[-1]
+        except (IndexError, ValueError):
+            # cannot handle very large and very small time intervals
+            return super().tickValues(minVal, maxVal, size)
+
+        ticks = bins.thresholds
+
+        max_steps = max(int(size / self._label_width), 1)
+        if len(ticks) > max_steps:
+            # remove some of ticks so that they don't overlap
+            step = int(np.ceil(float(len(ticks)) / max_steps))
+            ticks = ticks[::step]
+
+        spacing = min(b - a for a, b in zip(ticks[:-1], ticks[1:]))
+        return [(spacing, ticks)]
+
+    def tickStrings(self, values, scale, spacing):
+        """Format tick values according to space between them."""
+        if not self._use_time:
+            return super().tickStrings(values, scale, spacing)
+
+        if spacing >= 3600 * 24 * 365:
+            fmt = "%Y"
+        elif spacing >= 3600 * 24 * 28:
+            fmt = "%Y %b"
+        elif spacing >= 3600 * 24:
+            fmt = "%Y %b %d"
+        elif spacing >= 3600:
+            fmt = "%d %Hh"
+        elif spacing >= 60:
+            fmt = "%H:%M"
+        elif spacing >= 1:
+            fmt = "%H:%M:%S"
+        else:
+            fmt = '%S.%f'
+
+        # if timezone is not set, then local timezone is used
+        # which cause exceptions for edge cases
+        return [datetime.fromtimestamp(x, tz=timezone.utc).strftime(fmt)
+                for x in values]
+
+
 class OWScatterPlotBase(gui.OWComponent, QObject):
     """
     Provide a graph component for widgets that show any kind of point plot
@@ -408,8 +482,9 @@ def __init__(self, scatter_widget, parent=None, view_box=ViewBox):
         self.subset_is_shown = False
 
         self.view_box = view_box(self)
+        _axis = {"left": AxisItem("left"), "bottom": AxisItem("bottom")}
         self.plot_widget = pg.PlotWidget(viewBox=self.view_box, parent=parent,
-                                         background="w")
+                                         background="w", axisItems=_axis)
         self.plot_widget.hideAxis("left")
         self.plot_widget.hideAxis("bottom")
         self.plot_widget.getPlotItem().buttonsHidden = True

Orange/widgets/visualize/tests/test_owscatterplot.py

@@ -8,7 +8,9 @@
 from AnyQt.QtWidgets import QToolTip
 from AnyQt.QtGui import QColor
 
-from Orange.data import Table, Domain, ContinuousVariable, DiscreteVariable
+from Orange.data import (
+    Table, Domain, ContinuousVariable, DiscreteVariable, TimeVariable
+)
 from Orange.widgets.tests.base import (
     WidgetTest, WidgetOutputsTestMixin, datasets, ProjectionWidgetTestMixin
 )
@@ -1074,6 +1076,31 @@ def test_update_regression_line_is_called(self):
         urline.assert_called_once()
         urline.reset_mock()
 
+    def test_time_axis(self):
+        a = np.array([[1581953776, 1], [1581963776, 2], [1582953776, 3]])
+        d1 = Domain([ContinuousVariable("time"), ContinuousVariable("value")])
+        data = Table.from_numpy(d1, a)
+        d2 = Domain([TimeVariable("time"), ContinuousVariable("value")])
+        data_time = Table.from_numpy(d2, a)
+
+        x_axis = self.widget.graph.plot_widget.plotItem.getAxis("bottom")
+
+        self.send_signal(self.widget.Inputs.data, data)
+        self.assertFalse(x_axis._use_time)
+        _ticks = x_axis.tickValues(1581953776, 1582953776, 1000)
+        ticks = x_axis.tickStrings(_ticks[0][1], 1, _ticks[0][0])
+        try:
+            float(ticks[0])
+        except ValueError:
+            self.fail("axis should display floats")
+
+        self.send_signal(self.widget.Inputs.data, data_time)
+        self.assertTrue(x_axis._use_time)
+        _ticks = x_axis.tickValues(1581953776, 1582953776, 1000)
+        ticks = x_axis.tickStrings(_ticks[0][1], 1, _ticks[0][0])
+        with self.assertRaises(ValueError):
+            float(ticks[0])
+
 
 if __name__ == "__main__":
     import unittest