[FIX] ZeroDivisionError owmosaic.py

ZeroDivisionError should not be thrown when a column with only NaN-s is loaded into widget.
https://sentry.io/biolab/orange3/issues/204400244/

Corrects the total value and rectangles' widths.

Author: jerneju

Orange/widgets/visualize/owmosaic.py

@@ -512,6 +512,20 @@ def update_graph(self):
         spacing = self.SPACING
         bar_width = self.BAR_WIDTH
 
+        def get_counts(attr_vals, values):
+            """This function calculates rectangles' widths.
+            If all widths are zero then all widths are set to 1."""
+            if attr_vals == "":
+                counts = [conditionaldict[val] for val in values]
+            else:
+                counts = [conditionaldict[attr_vals + "-" + val]
+                          for val in values]
+            total = sum(counts)
+            if total == 0:
+                counts = [1] * len(values)
+                total = sum(counts)
+            return total, counts
+
         def draw_data(attr_list, x0_x1, y0_y1, side, condition,
                       total_attrs, used_attrs, used_vals, attr_vals=""):
             x0, x1 = x0_x1
@@ -542,12 +556,7 @@ def draw_data(attr_list, x0_x1, y0_y1, side, condition,
                 if whole == 0:
                     edge = (y1 - y0) / float(len(values) - 1)
 
-            if attr_vals == "":
-                counts = [conditionaldict[val] for val in values]
-            else:
-                counts = [conditionaldict[attr_vals + "-" + val]
-                          for val in values]
-            total = sum(counts)
+            total, counts = get_counts(attr_vals, values)
 
             # if we are visualizing the third attribute and the first attribute
             # has the last value, we have to reverse the order in which the
@@ -633,15 +642,7 @@ def draw_text(side, attr, x0_x1, y0_y1,
             # calculate position of first attribute
             currpos = 0
 
-            if attr_vals == "":
-                counts = [conditionaldict.get(val, 1) for val in values]
-            else:
-                counts = [conditionaldict.get(attr_vals + "-" + val, 1)
-                          for val in values]
-            total = sum(counts)
-            if total == 0:
-                counts = [1] * len(values)
-                total = sum(counts)
+            total, counts = get_counts(attr_vals, values)
 
             aligns = [Qt.AlignTop | Qt.AlignHCenter,
                       Qt.AlignRight | Qt.AlignVCenter,

Orange/widgets/visualize/tests/test_owmosaic.py

@@ -7,7 +7,7 @@
 
 from Orange.data import Table, DiscreteVariable, Domain, ContinuousVariable
 from Orange.widgets.tests.base import WidgetTest, WidgetOutputsTestMixin
-from Orange.widgets.visualize.owmosaic import OWMosaicDisplay, MosaicVizRank
+from Orange.widgets.visualize.owmosaic import OWMosaicDisplay
 
 
 class TestOWMosaicDisplay(WidgetTest, WidgetOutputsTestMixin):
@@ -194,3 +194,21 @@ def test_does_not_crash(self):
         data = Table("housing.tab")
         widget.set_data(data)
         vizrank.toggle()
+
+    def test_nan_column(self):
+        """
+        A column with only NaN-s used to throw an error
+        (ZeroDivisionError) when loaded into widget.
+        GH-2046
+        """
+        table = Table(
+            Domain(
+                [ContinuousVariable("a"), ContinuousVariable("b"), ContinuousVariable("c")]),
+            np.array([
+                [0, np.NaN, 0],
+                [0, np.NaN, 0],
+                [0, np.NaN, 0]
+            ])
+        )
+        self.send_signal("Data", table)
+