fix plot_scatter error with 0 or 1 points (and 2 points with extent) (c…

…loses #197)

src/flowkit/_utils/plot_utils.py

@@ -377,8 +377,18 @@ def plot_scatter(
 
     if len(x) > 0:
         x_min, x_max = _calculate_extent(x, d_min=x_min, d_max=x_max, pad=0.02)
+    else:
+        # empty array, set extents to 0 to avoid errors
+        x_min = x_max = 0
+
+        # turn off color density
+        color_density = False
+
     if len(y) > 0:
         y_min, y_max = _calculate_extent(y, d_min=y_min, d_max=y_max, pad=0.02)
+    else:
+        # empty array, set extents to 0 to avoid errors
+        y_min = y_max = 0
 
     if y_max > x_max:
         radius_dimension = 'y'
@@ -444,7 +454,11 @@ def plot_scatter(
             # re-order the highlight indices to match
             highlight_mask = highlight_mask[idx]
 
-        z_norm = (z - z.min()) / (z.max() - z.min())
+        # check if z max - z min is 0 (e.g. a single data point)
+        if z.max() - z.min() == 0:
+            z_norm = np.zeros(len(x))
+        else:
+            z_norm = (z - z.min()) / (z.max() - z.min())
     else:
         z_norm = np.zeros(len(x))
 
@@ -477,15 +491,16 @@ def plot_scatter(
     p.xaxis.axis_label = x_label
     p.yaxis.axis_label = y_label
 
-    p.circle(
-        x,
-        y,
-        radius=radius,
-        radius_dimension=radius_dimension,
-        fill_color=z_colors,
-        fill_alpha=fill_alpha,
-        line_color=None
-    )
+    if len(x) > 0:
+        p.circle(
+            x,
+            y,
+            radius=radius,
+            radius_dimension=radius_dimension,
+            fill_color=z_colors,
+            fill_alpha=fill_alpha,
+            line_color=None
+        )
 
     return p
 

tests/plot_tests.py

@@ -3,6 +3,9 @@
 """
 import copy
 import unittest
+
+import bokeh.models
+import numpy as np
 from bokeh.plotting import figure as bk_Figure
 from bokeh.layouts import GridPlot as bk_GridPlot
 import flowkit as fk
@@ -21,6 +24,32 @@ class PlotTestCase(unittest.TestCase):
           pixel-level, this TestCase only tests that plots are returned
           from plotting functions.
     """
+    def test_plot_scatter_zero_points(self):
+        # from issue #197
+        arr = np.array([], float)
+        # noinspection PyProtectedMember
+        p = fk._utils.plot_utils.plot_scatter(arr, arr)
+
+        self.assertIsInstance(p, bk_Figure)
+
+    def test_plot_scatter_one_point(self):
+        # from issue #197
+        arr = np.array([1., ], float)
+        # noinspection PyProtectedMember
+        p = fk._utils.plot_utils.plot_scatter(arr, arr)
+
+        self.assertIsInstance(p, bk_Figure)
+
+    def test_plot_scatter_two_points_with_extents(self):
+        # from issue #197
+        # noinspection PyProtectedMember
+        p = fk._utils.plot_utils.plot_scatter(
+            np.array([0.44592386, 0.52033713]),
+            np.array([0.6131338, 0.60149982]),
+            x_min=0, x_max=.997, y_min=0, y_max=.991
+        )
+
+        self.assertIsInstance(p, bk_Figure)
 
     def test_sample_plot_histogram(self):
         sample = copy.deepcopy(test_sample)