tlkaufmann · Feb 7, 2022 · May 2, 2022 · May 2, 2022 · Dec 16, 2022 · Dec 16, 2022
diff --git a/doc/users/next_whats_new/stackplot_artifacts.rst b/doc/users/next_whats_new/stackplot_artifacts.rst
@@ -0,0 +1,42 @@
+Suppress 0 thickness layers in stackplots
+-----------------------------------------
+
+When making `.Axes.stackplot` where one of the layers is 0 it may or may not be
+desirable for that layer to be visible.  Using the new *where* keyword argument
+along with the *interpolate* keyword argument these lines can be suppressed.
+
+
+.. plot::
+   :include-source: true
+
+   import matplotlib.pyplot as plt
+   import numpy as np
+
+   fig, (axl, axr) = plt.subplots(1, 2)
+
+   x = np.arange(10)
+
+   colors = ["grey", "blue", "red", "blue"]
+
+   y = np.stack(
+       [
+           np.linspace(0, 1, 10),
+           np.linspace(0, 1, 10),
+           [0, 0, 0.25, 0, 0, 0, 0.25, 0, 0, 0],
+           np.linspace(0, 1, 10),
+       ]
+   )
+
+   axl.set_title("No line")
+   axl.stackplot(
+       x, y,
+       colors=colors, edgecolor="face",
+       where=(y != 0), interpolate=True,
+   )
+
+
+   axr.set_title("With line")
+   axr.stackplot(
+       x, y,
+       colors=colors, edgecolor="face",
+   )
diff --git a/lib/matplotlib/pyplot.py b/lib/matplotlib/pyplot.py
@@ -2872,11 +2872,12 @@ def spy(
 # Autogenerated by boilerplate.py.  Do not edit as changes will be lost.
 @_copy_docstring_and_deprecators(Axes.stackplot)
 def stackplot(
-        x, *args, labels=(), colors=None, baseline='zero', data=None,
-        **kwargs):
+        x, *args, labels=(), colors=None, baseline='zero',
+        where=None, data=None, **kwargs):
     return gca().stackplot(
         x, *args, labels=labels, colors=colors, baseline=baseline,
-        **({"data": data} if data is not None else {}), **kwargs)
+        where=where, **({"data": data} if data is not None else {}),
+        **kwargs)
 
 
 # Autogenerated by boilerplate.py.  Do not edit as changes will be lost.

diff --git a/lib/matplotlib/stackplot.py b/lib/matplotlib/stackplot.py
@@ -16,7 +16,7 @@
 
 
 def stackplot(axes, x, *args,
-              labels=(), colors=None, baseline='zero',
+              labels=(), colors=None, baseline='zero', where=None,
               **kwargs):
     """
     Draw a stacked area plot.
@@ -58,6 +58,15 @@ def stackplot(axes, x, *args,
     data : indexable object, optional
         DATA_PARAMETER_PLACEHOLDER
 
+    where: bool or array of bool, optional
+        Passed to `.Axes.fill_between` and defines where to exclude horizontal
+        regions from being filled. The filled regions are defined by the
+        coordinates ``x[where]``. Can be either a single bool, an array of
+        shape (N,) or an array of shape (M, N).  Should be used together with
+        kwarg ``interpolate=True``.
+
+        .. versionadded:: 3.7
+
     **kwargs
         All other keyword arguments are passed to `.Axes.fill_between`.
 
@@ -66,10 +75,19 @@ def stackplot(axes, x, *args,
     list of `.PolyCollection`
         A list of `.PolyCollection` instances, one for each element in the
         stacked area plot.
+
     """
 
     y = np.row_stack(args)
 
+    if where is not None:
+        if kwargs.get('interpolate', False) is False:
+            _api.warn_external('Argument where should be used together with '
+                               'kwarg interpolate=True')
+    else:
+        where = True
+    where = np.broadcast_to(where, np.shape(y))
+
     labels = iter(labels)
     if colors is not None:
         colors = itertools.cycle(colors)
@@ -114,6 +132,7 @@ def stackplot(axes, x, *args,
     # Color between x = 0 and the first array.
     coll = axes.fill_between(x, first_line, stack[0, :],
                              facecolor=next(colors), label=next(labels, None),
+                             where=where[0, :],
                              **kwargs)
     coll.sticky_edges.y[:] = [0]
     r = [coll]
@@ -123,5 +142,6 @@ def stackplot(axes, x, *args,
         r.append(axes.fill_between(x, stack[i, :], stack[i + 1, :],
                                    facecolor=next(colors),
                                    label=next(labels, None),
+                                   where=where[i+1, :],
                                    **kwargs))
     return r
diff --git a/lib/matplotlib/tests/baseline_images/test_axes/stackplot_test_where.pdf b/lib/matplotlib/tests/baseline_images/test_axes/stackplot_test_where.pdf
diff --git a/lib/matplotlib/tests/baseline_images/test_axes/stackplot_test_where.png b/lib/matplotlib/tests/baseline_images/test_axes/stackplot_test_where.png