From 1a85e2d1ff97ccf18359d6bbcb24ecca10e543eb Mon Sep 17 00:00:00 2001
From: David Stansby <dstansby@gmail.com>
Date: Tue, 24 Oct 2017 20:29:01 +0100
Subject: [PATCH] Improve step performance

---
 doc/api/api_changes/2017-10-24-DS.rst         |  10 ++++++
 lib/matplotlib/axes/_axes.py                  |  13 ++++---
 lib/matplotlib/container.py                   |  11 ++++--
 lib/matplotlib/legend_handler.py              |  34 ++++++++++++------
 .../tests/baseline_images/test_axes/stem.png  | Bin 0 -> 14306 bytes
 lib/matplotlib/tests/test_axes.py             |  11 ++++++
 6 files changed, 61 insertions(+), 18 deletions(-)
 create mode 100644 doc/api/api_changes/2017-10-24-DS.rst
 create mode 100644 lib/matplotlib/tests/baseline_images/test_axes/stem.png

diff --git a/doc/api/api_changes/2017-10-24-DS.rst b/doc/api/api_changes/2017-10-24-DS.rst
new file mode 100644
index 000000000000..c1c3c6ec9c55
--- /dev/null
+++ b/doc/api/api_changes/2017-10-24-DS.rst
@@ -0,0 +1,10 @@
+`StemContainer` now stores `LineCollection`
+-------------------------------------------
+
+`StemContainer` objects now store a `LineCollection` object instead of a list
+of `Line2D` objects for stem lines plotted using `ax.stem`. This gives a very
+large performance boost to displaying and moving `ax.stem` plots.
+
+Line segments can be extracted from the `LineCollection` using
+`LineCollection.get_segements()`. See the `LineCollection` documentation for
+other methods to retrieve the collection properties.
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
index 9fa6e6650b00..67d5d5007aa1 100644
--- a/lib/matplotlib/axes/_axes.py
+++ b/lib/matplotlib/axes/_axes.py
@@ -2370,6 +2370,9 @@ def stem(self, *args, linefmt=None, markerfmt=None, basefmt=None,
             x = y
             y = np.asarray(args[0], dtype=float)
             args = args[1:]
+        self._process_unit_info(xdata=x, ydata=y)
+        x = self.convert_xunits(x)
+        y = self.convert_yunits(y)
 
         # defaults for formats
         if linefmt is None:
@@ -2421,12 +2424,12 @@ def stem(self, *args, linefmt=None, markerfmt=None, basefmt=None,
         markerline, = self.plot(x, y, color=markercolor, linestyle=markerstyle,
                                 marker=markermarker, label="_nolegend_")
 
-        stemlines = []
+        lines = []
         for thisx, thisy in zip(x, y):
-            l, = self.plot([thisx, thisx], [bottom, thisy],
-                           color=linecolor, linestyle=linestyle,
-                           marker=linemarker, label="_nolegend_")
-            stemlines.append(l)
+            lines.append(((thisx, bottom), (thisx, thisy)))
+        stemlines = mcoll.LineCollection(lines, linestyles=linestyle,
+                                         colors=linecolor, label='_nolegend_')
+        self.add_collection(stemlines)
 
         baseline, = self.plot([np.min(x), np.max(x)], [bottom, bottom],
                               color=basecolor, linestyle=basestyle,
diff --git a/lib/matplotlib/container.py b/lib/matplotlib/container.py
index 552d6da5a761..0f71c606fe5c 100644
--- a/lib/matplotlib/container.py
+++ b/lib/matplotlib/container.py
@@ -174,10 +174,17 @@ class StemContainer(Container):
 
     baseline : :class:`~matplotlib.lines.Line2D`
         The artist of the horizontal baseline.
-
     """
-
     def __init__(self, markerline_stemlines_baseline, **kwargs):
+        '''
+        Parameters
+        ----------
+        markerline_stemlines_baseline : tuple
+            Tuple of ``(markerline, stemlines, baseline)``.
+            ``markerline`` contains the `LineCollection` of the markers,
+            ``stemlines`` is a `LineCollection` of the main lines,
+            ``baseline`` is the `Line2D` of the baseline.
+        '''
         markerline, stemlines, baseline = markerline_stemlines_baseline
         self.markerline = markerline
         self.stemlines = stemlines
diff --git a/lib/matplotlib/legend_handler.py b/lib/matplotlib/legend_handler.py
index ad574dcf33d0..44f1afc0b236 100644
--- a/lib/matplotlib/legend_handler.py
+++ b/lib/matplotlib/legend_handler.py
@@ -589,7 +589,6 @@ def get_ydata(self, legend, xdescent, ydescent, width, height, fontsize):
     def create_artists(self, legend, orig_handle,
                        xdescent, ydescent, width, height, fontsize,
                        trans):
-
         markerline, stemlines, baseline = orig_handle
 
         xdata, xdata_marker = self.get_xdata(legend, xdescent, ydescent,
@@ -603,31 +602,44 @@ def create_artists(self, legend, orig_handle,
         else:
             bottom = self._bottom
 
-        leg_markerline = Line2D(xdata_marker, ydata[:len(xdata_marker)])
-        self.update_prop(leg_markerline, markerline, legend)
-
         leg_stemlines = []
-        for thisx, thisy in zip(xdata_marker, ydata):
-            l = Line2D([thisx, thisx], [bottom, thisy])
-            leg_stemlines.append(l)
 
-        for lm, m in zip(leg_stemlines, stemlines):
-            self.update_prop(lm, m, legend)
+        # update_prop() usually takes two Line2D collections;
+        # override temporarily to copy properties from a LineCollection
+        orig_update_func = self._update_prop_func
+        self._update_prop_func = self._copy_collection_props
+
+        for thisx, thisy in zip(xdata_marker, ydata):
+            thisline = Line2D([thisx, thisx], [bottom, thisy])
+            leg_stemlines.append(thisline)
+            self.update_prop(thisline, stemlines, legend)
+        # Reset update_prop_func
+        self._update_prop_func = orig_update_func
 
         leg_baseline = Line2D([np.min(xdata), np.max(xdata)],
                               [bottom, bottom])
 
         self.update_prop(leg_baseline, baseline, legend)
 
-        artists = [leg_markerline]
-        artists.extend(leg_stemlines)
+        leg_markerline = Line2D(xdata_marker, ydata[:len(xdata_marker)])
+        self.update_prop(leg_markerline, markerline, legend)
+
+        artists = leg_stemlines
         artists.append(leg_baseline)
+        artists.append(leg_markerline)
 
         for artist in artists:
             artist.set_transform(trans)
 
         return artists
 
+    def _copy_collection_props(self, legend_handle, orig_handle):
+        '''
+        Method to copy properties from a LineCollection (orig_handle) to a
+        Line2D (legend_handle).
+        '''
+        legend_handle._color = orig_handle.get_color()[0]
+
 
 class HandlerTuple(HandlerBase):
     """
diff --git a/lib/matplotlib/tests/baseline_images/test_axes/stem.png b/lib/matplotlib/tests/baseline_images/test_axes/stem.png
new file mode 100644
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HcmV?d00001

diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
index 12197bd8e55f..8a6515dbe045 100644
--- a/lib/matplotlib/tests/test_axes.py
+++ b/lib/matplotlib/tests/test_axes.py
@@ -2876,6 +2876,17 @@ def test_hist_stacked_weighted():
     ax.hist((d1, d2), weights=(w1, w2), histtype="stepfilled", stacked=True)
 
 
+@image_comparison(baseline_images=['stem'], extensions=['png'], style='mpl20',
+                  remove_text=True)
+def test_stem():
+    x = np.linspace(0.1, 2 * np.pi, 100)
+
+    fig, ax = plt.subplots()
+    ax.stem(x, np.cos(x), linefmt='C2-', markerfmt='k+', basefmt='C1-.',
+            label='Stem')
+    ax.legend()
+
+
 def test_stem_args():
     fig = plt.figure()
     ax = fig.add_subplot(1, 1, 1)