Set alpha properly on unfilled hist/kde plots (#2460)

* Set alpha properly on unfilled hist/kde plots

Fixes #2450

* Fix typo in kdeplot docstring

* Generalize color comparison

doc/releases/v0.12.0.txt

@@ -20,6 +20,8 @@ v0.12.0 (Unreleased)
 
 - |Fix| In :func:`rugplot`, fixed a bug that prevented the use of datetime data (:pr:`2458`).
 
+- |Fix| In :func:`histplot` and :func:`kdeplot`, fixed a bug where the `alpha` parameter was ignored when `fill=False` (:pr:`2460`).
+
 - |Fix| |Enhancement| Improved integration with the matplotlib color cycle in most axes-level functions (:pr:`2449`).
 
 - Made `scipy` an optional dependency and added `pip install seaborn[all]` as a method for ensuring the availability of compatible `scipy` and `statsmodels` libraries at install time. This has a few minor implications for existing code, which are explained in the Github pull request (:pr:`2398`).

seaborn/_statistics.py

@@ -65,7 +65,7 @@ def __init__(
             Factor, multiplied by the smoothing bandwidth, that determines how
             far the evaluation grid extends past the extreme datapoints. When
             set to 0, truncate the curve at the data limits.
-        clip : pair of numbers None, or a pair of such pairs
+        clip : pair of numbers or None, or a pair of such pairs
             Do not evaluate the density outside of these limits.
         cumulative : bool, optional
             If True, estimate a cumulative distribution function. Requires scipy.

seaborn/_testing.py

@@ -1,5 +1,6 @@
 import numpy as np
 import matplotlib as mpl
+from matplotlib.colors import to_rgb, to_rgba
 from numpy.testing import assert_array_equal
 
 
@@ -69,3 +70,21 @@ def assert_plots_equal(ax1, ax2, labels=True):
     if labels:
         assert ax1.get_xlabel() == ax2.get_xlabel()
         assert ax1.get_ylabel() == ax2.get_ylabel()
+
+
+def assert_colors_equal(a, b, check_alpha=True):
+
+    def handle_array(x):
+
+        if isinstance(x, np.ndarray):
+            if x.ndim > 1:
+                x = np.unique(x, axis=0).squeeze()
+            if x.ndim > 1:
+                raise ValueError("Color arrays must be 1 dimensional")
+        return x
+
+    a = handle_array(a)
+    b = handle_array(b)
+
+    f = to_rgba if check_alpha else to_rgb
+    assert f(a) == f(b)

seaborn/distributions.py

@@ -185,9 +185,9 @@ def _artist_kws(self, kws, fill, element, multiple, color, alpha):
                 kws.setdefault("edgecolor", to_rgba(color, 1))
         elif element == "bars":
             kws["facecolor"] = "none"
-            kws["edgecolor"] = to_rgba(color, 1)
+            kws["edgecolor"] = to_rgba(color, alpha)
         else:
-            kws["color"] = color
+            kws["color"] = to_rgba(color, alpha)
         return kws
 
     def _quantile_to_level(self, data, quantile):
@@ -502,12 +502,15 @@ def plot_univariate_histogram(
         # Note: default linewidth is determined after plotting
 
         # Default alpha should depend on other parameters
-        if multiple == "layer":
-            default_alpha = .5 if element == "bars" else .25
-        elif kde:
-            default_alpha = .5
+        if fill:
+            if multiple == "layer":
+                default_alpha = .5 if element == "bars" else .25
+            elif kde:
+                default_alpha = .5
+            else:
+                default_alpha = .75
         else:
-            default_alpha = .75
+            default_alpha = 1
         alpha = plot_kws.pop("alpha", default_alpha)  # TODO make parameter?
 
         hist_artists = []
@@ -914,7 +917,10 @@ def plot_univariate_density(
             sticky_support = []
 
         # XXX unfilled kdeplot is ignoring
-        default_alpha = .25 if multiple == "layer" else .75
+        if fill:
+            default_alpha = .25 if multiple == "layer" else .75
+        else:
+            default_alpha = 1
         alpha = plot_kws.pop("alpha", default_alpha)  # TODO make parameter?
 
         # Now iterate through the subsets and draw the densities

seaborn/tests/test_axisgrid.py

@@ -20,6 +20,7 @@
 from .. import axisgrid as ag
 from .._testing import (
     assert_plots_equal,
+    assert_colors_equal,
 )
 
 rs = np.random.RandomState(0)
@@ -224,7 +225,7 @@ def test_legend_data(self):
         assert len(lines) == len(a_levels)
 
         for line, hue in zip(lines, palette):
-            assert line.get_color() == hue
+            assert_colors_equal(line.get_color(), hue)
 
         labels = g._legend.get_texts()
         assert len(labels) == len(a_levels)
@@ -249,7 +250,7 @@ def test_legend_data_missing_level(self):
         assert len(lines) == len(a_levels)
 
         for line, hue in zip(lines, palette):
-            assert line.get_color() == hue
+            assert_colors_equal(line.get_color(), hue)
 
         labels = g._legend.get_texts()
         assert len(labels) == 4
@@ -273,7 +274,7 @@ def test_get_boolean_legend_data(self):
         assert len(lines) == len(b_levels)
 
         for line, hue in zip(lines, palette):
-            assert line.get_color() == hue
+            assert_colors_equal(line.get_color(), hue)
 
         labels = g._legend.get_texts()
         assert len(labels) == len(b_levels)
@@ -941,21 +942,20 @@ def test_map_diag_rectangular(self):
     def test_map_diag_color(self):
 
         color = "red"
-        rgb_color = mpl.colors.colorConverter.to_rgba(color)
 
         g1 = ag.PairGrid(self.df)
         g1.map_diag(plt.hist, color=color)
 
         for ax in g1.diag_axes:
             for patch in ax.patches:
-                assert patch.get_facecolor() == rgb_color
+                assert_colors_equal(patch.get_facecolor(), color)
 
         g2 = ag.PairGrid(self.df)
         g2.map_diag(kdeplot, color='red')
 
         for ax in g2.diag_axes:
             for line in ax.lines:
-                assert line.get_color() == color
+                assert_colors_equal(line.get_color(), color)
 
     def test_map_diag_palette(self):
 
@@ -966,7 +966,7 @@ def test_map_diag_palette(self):
 
         for ax in g.diag_axes:
             for line, color in zip(ax.lines[::-1], pal):
-                assert line.get_color() == color
+                assert_colors_equal(line.get_color(), color)
 
     def test_map_diag_and_offdiag(self):
 
@@ -1656,12 +1656,11 @@ def test_color(self):
 
         g = ag.jointplot(x="x", y="y", data=self.data, color="purple")
 
-        purple = mpl.colors.colorConverter.to_rgb("purple")
-        scatter_color = g.ax_joint.collections[0].get_facecolor()[0, :3]
-        assert tuple(scatter_color) == purple
+        scatter_color = g.ax_joint.collections[0].get_facecolor()
+        assert_colors_equal(scatter_color, "purple")
 
         hist_color = g.ax_marg_x.patches[0].get_facecolor()[:3]
-        assert hist_color == purple
+        assert_colors_equal(hist_color, "purple")
 
     def test_palette(self, long_df):