[ENH] HeatMap: Allow setting the center when using diverging palettes

Orange/widgets/utils/colorgradientselection.py

@@ -2,26 +2,29 @@
 
 from AnyQt.QtCore import Qt, QSize, QAbstractItemModel, Property
 from AnyQt.QtWidgets import (
-    QWidget, QSlider, QFormLayout, QComboBox, QStyle
-)
+    QWidget, QSlider, QFormLayout, QComboBox, QStyle,
+    QHBoxLayout, QLineEdit, QLabel)
 from AnyQt.QtCore import Signal
+from AnyQt.QtGui import QFontMetrics, QDoubleValidator
 
-from Orange.widgets.utils import itemmodels
+from Orange.widgets.utils import itemmodels, colorpalettes
 
 
 class ColorGradientSelection(QWidget):
     activated = Signal(int)
 
     currentIndexChanged = Signal(int)
     thresholdsChanged = Signal(float, float)
+    centerChanged = Signal(float)
 
-    def __init__(self, *args, thresholds=(0.0, 1.0), **kwargs):
+    def __init__(self, *args, thresholds=(0.0, 1.0), center=None, **kwargs):
         super().__init__(*args, **kwargs)
 
         low = round(clip(thresholds[0], 0., 1.), 2)
         high = round(clip(thresholds[1], 0., 1.), 2)
         high = max(low, high)
         self.__threshold_low, self.__threshold_high = low, high
+        self.__center = center
         form = QFormLayout(
             formAlignment=Qt.AlignLeft,
             labelAlignment=Qt.AlignLeft,
@@ -43,6 +46,29 @@ def __init__(self, *args, thresholds=(0.0, 1.0), **kwargs):
         self.gradient_cb.activated[int].connect(self.activated)
         self.gradient_cb.currentIndexChanged.connect(self.currentIndexChanged)
 
+        if center is not None:
+            def __on_center_changed():
+                self.__center = float(self.center_edit.text() or "0")
+                self.centerChanged.emit(self.__center)
+
+            self.center_box = QWidget()
+            center_layout = QHBoxLayout()
+            self.center_box.setLayout(center_layout)
+            width = QFontMetrics(self.font()).boundingRect("9999999").width()
+            self.center_edit = QLineEdit(
+                text=f"{self.__center}",
+                maximumWidth=width, placeholderText="0", alignment=Qt.AlignRight)
+            self.center_edit.setValidator(QDoubleValidator())
+            self.center_edit.editingFinished.connect(__on_center_changed)
+            center_layout.setContentsMargins(0, 0, 0, 0)
+            center_layout.addStretch(1)
+            center_layout.addWidget(QLabel("Centered at"))
+            center_layout.addWidget(self.center_edit)
+            self.gradient_cb.currentIndexChanged.connect(
+                self.__update_center_visibility)
+        else:
+            self.center_box = None
+
         slider_low = QSlider(
             objectName="threshold-low-slider", minimum=0, maximum=100,
             value=int(low * 100), orientation=Qt.Horizontal,
@@ -60,6 +86,8 @@ def __init__(self, *args, thresholds=(0.0, 1.0), **kwargs):
                               "gradient from the higher end")
         )
         form.setWidget(0, QFormLayout.SpanningRole, self.gradient_cb)
+        if self.center_box:
+            form.setWidget(1, QFormLayout.SpanningRole, self.center_box)
         form.addRow(self.tr("Low:"), slider_low)
         form.addRow(self.tr("High:"), slider_high)
         self.slider_low = slider_low
@@ -79,6 +107,7 @@ def findData(self, data: Any, role: Qt.ItemDataRole) -> int:
 
     def setCurrentIndex(self, index: int) -> None:
         self.gradient_cb.setCurrentIndex(index)
+        self.__update_center_visibility()
 
     def currentIndex(self) -> int:
         return self.gradient_cb.currentIndex()
@@ -109,6 +138,14 @@ def thresholdHigh(self) -> float:
     def setThresholdHigh(self, high: float) -> None:
         self.setThresholds(min(self.__threshold_low, high), high)
 
+    def center(self) -> float:
+        return self.__center
+
+    def setCenter(self, center: float) -> None:
+        self.__center = center
+        self.center_edit.setText(f"{center}")
+        self.centerChanged.emit(center)
+
     thresholdHigh_ = Property(
         float, thresholdLow, setThresholdLow, notify=thresholdsChanged)
 
@@ -146,6 +183,15 @@ def setThresholds(self, low: float, high: float) -> None:
             self.slider_high.setSliderPosition(high * 100)
             self.thresholdsChanged.emit(high, low)
 
+    def __update_center_visibility(self):
+        if self.center_box is None:
+            return
+
+        palette = self.currentData()
+        self.center_box.setVisible(
+            isinstance(palette, colorpalettes.Palette)
+            and palette.flags & palette.Flags.Diverging != 0)
+
 
 def clip(a, amin, amax):
     return min(max(a, amin), amax)

Orange/widgets/utils/tests/test_colorgradientselection.py

@@ -1,11 +1,15 @@
+from unittest.mock import Mock
+
 import numpy as np
 
 from AnyQt.QtTest import QSignalSpy
-from AnyQt.QtCore import Qt, QStringListModel
+from AnyQt.QtCore import Qt, QStringListModel, QModelIndex
 
+from Orange.widgets.utils import itemmodels
 from Orange.widgets.utils.colorgradientselection import ColorGradientSelection
 from Orange.widgets.tests.base import GuiTest
 
+
 class TestColorGradientSelection(GuiTest):
     def test_constructor(self):
         w = ColorGradientSelection(thresholds=(0.1, 0.9))
@@ -68,3 +72,40 @@ def test_slider_move(self):
         low, high = changed[-1]
         self.assertLessEqual(low, high)
         self.assertEqual(high, 0.0)
+
+    def test_center(self):
+        w = ColorGradientSelection(center=42)
+        self.assertEqual(w.center(), 42)
+        w.setCenter(40)
+        self.assertEqual(w.center(), 40)
+
+    def test_center_visibility(self):
+        w = ColorGradientSelection(center=0)
+        w.center_box.setVisible = Mock()
+        model = itemmodels.ContinuousPalettesModel()
+        w.setModel(model)
+        for row in range(model.rowCount(QModelIndex())):
+            palette = model.data(model.index(row, 0), Qt.UserRole)
+            if palette:
+                if palette.flags & palette.Diverging:
+                    diverging = row
+                else:
+                    nondiverging = row
+
+        w.setCurrentIndex(diverging)
+        w.center_box.setVisible.assert_called_with(True)
+        w.setCurrentIndex(nondiverging)
+        w.center_box.setVisible.assert_called_with(False)
+        w.setCurrentIndex(diverging)
+        w.center_box.setVisible.assert_called_with(True)
+
+        w = ColorGradientSelection()
+        self.assertIsNone(w.center_box)
+
+    def test_center_changed(self):
+        w = ColorGradientSelection(center=42)
+        changed = QSignalSpy(w.centerChanged)
+        w.center_edit.setText("41")
+        w.center_edit.editingFinished.emit()
+        self.assertEqual(w.center(), 41)
+        self.assertEqual(list(changed), [[41]])

Orange/widgets/visualize/owheatmap.py

@@ -155,6 +155,7 @@ class Outputs:
 
     threshold_low = settings.Setting(0.0)
     threshold_high = settings.Setting(1.0)
+    color_center = settings.Setting(0)
 
     merge_kmeans = settings.Setting(False)
     merge_kmeans_k = settings.Setting(50)
@@ -202,6 +203,12 @@ class Error(widget.OWWidget.Error):
     class Warning(widget.OWWidget.Warning):
         empty_clusters = Msg("Empty clusters were removed")
 
+    UserAdviceMessages = [
+        widget.Message(
+            "For data with a meaningful mid-point, "
+            "choose one of diverging palettes.",
+            "diverging_palette")]
+
     def __init__(self):
         super().__init__()
         self.__pending_selection = self.selected_rows
@@ -244,6 +251,7 @@ def _():
 
         self.color_map_widget = cmw = ColorGradientSelection(
             thresholds=(self.threshold_low, self.threshold_high),
+            center=self.color_center
         )
         model = itemmodels.ContinuousPalettesModel(parent=self)
         cmw.setModel(model)
@@ -257,6 +265,12 @@ def _set_thresholds(low, high):
             self.threshold_low, self.threshold_high = low, high
             self.update_color_schema()
         cmw.thresholdsChanged.connect(_set_thresholds)
+
+        def _set_centering(center):
+            self.color_center = center
+            self.update_color_schema()
+        cmw.centerChanged.connect(_set_centering)
+
         colorbox.layout().addWidget(self.color_map_widget)
 
         mergebox = gui.vBox(self.controlArea, "Merge",)
@@ -449,7 +463,7 @@ def color_palette(self):
     def color_map(self) -> GradientColorMap:
         return GradientColorMap(
             self.color_palette(), (self.threshold_low, self.threshold_high),
-            0 if self.center_palette else None
+            self.color_map_widget.center() if self.center_palette else None
         )
 
     def clear(self):

Orange/widgets/visualize/tests/test_owheatmap.py

@@ -2,7 +2,7 @@
 # pylint: disable=missing-docstring, protected-access
 import warnings
 import unittest
-from unittest.mock import patch
+from unittest.mock import patch, Mock
 
 import numpy as np
 from sklearn.exceptions import ConvergenceWarning
@@ -245,6 +245,21 @@ def test_palette_centering(self):
                 colors = image_row_colors(image)
                 np.testing.assert_almost_equal(colors, desired)
 
+    def test_centering_threshold_change(self):
+        data = np.arange(2).reshape(-1, 1)
+        table = Table.from_numpy(Domain([ContinuousVariable("y")]), data)
+        self.send_signal(self.widget.Inputs.data, table)
+
+        cmw = self.widget.color_map_widget
+        palette_index = cmw.findData(
+            colorpalettes.ContinuousPalettes["diverging_bwr_40_95_c42"],
+            Qt.UserRole)
+        cmw.setCurrentIndex(palette_index)
+
+        self.widget.update_color_schema = Mock()
+        cmw.centerChanged.emit(42)
+        self.widget.update_color_schema.assert_called()
+
     def test_palette_center(self):
         widget = self.widget
         model = widget.color_map_widget.model()

doc/visual-programming/source/widgets/visualize/heatmap.md

@@ -15,7 +15,7 @@ Plots a heat map for a pair of attributes.
 
 ![](images/HeatMap-stamped.png)
 
-1. The color scheme legend. **Low** and **High** are thresholds for the color palette (low for attributes with low values and high for attributes with high values).
+1. The color scheme legend. **Low** and **High** are thresholds for the color palette (low for attributes with low values and high for attributes with high values). Selecting one of diverging palettes, which have two extreme colors and a neutral (black or white) color at the midpoint, enables an option to set a meaningful mid-point value (default is 0).
 2. Merge data.
 3. Sort columns and rows:
    - **No Sorting** (lists attributes as found in the dataset)