Merge pull request matplotlib#27605 from dstansby/masked-boxplot

Ignore masked values in boxplot

Author: timhoffm

doc/api/next_api_changes/behavior/27605-DS.rst

@@ -0,0 +1,4 @@
+Boxplots now ignore masked data points
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+`~matplotlib.axes.Axes.boxplot` and `~matplotlib.cbook.boxplot_stats` now ignore
+any masked points in the input data.

lib/matplotlib/cbook.py

@@ -1274,7 +1274,8 @@ def _compute_conf_interval(data, med, iqr, bootstrap):
             continue
 
         # up-convert to an array, just to be safe
-        x = np.asarray(x)
+        x = np.ma.asarray(x)
+        x = x.data[~x.mask].ravel()
 
         # arithmetic mean
         stats['mean'] = np.mean(x)

lib/matplotlib/tests/test_axes.py

@@ -3388,6 +3388,20 @@ def test_boxplot():
     ax.set_ylim((-30, 30))
 
 
+@check_figures_equal(extensions=["png"])
+def test_boxplot_masked(fig_test, fig_ref):
+    # Check that masked values are ignored when plotting a boxplot
+    x_orig = np.linspace(-1, 1, 200)
+
+    ax = fig_test.subplots()
+    x = x_orig[x_orig >= 0]
+    ax.boxplot(x)
+
+    x = np.ma.masked_less(x_orig, 0)
+    ax = fig_ref.subplots()
+    ax.boxplot(x)
+
+
 @image_comparison(['boxplot_custom_capwidths.png'],
                   savefig_kwarg={'dpi': 40}, style='default')
 def test_boxplot_custom_capwidths():