matplotlib · vecuenca · Mar 16, 2016 · Mar 17, 2016 · Mar 17, 2016 · Mar 17, 2016
diff --git a/doc/users/whats_new/stem_orientation.rst b/doc/users/whats_new/stem_orientation.rst
@@ -0,0 +1,10 @@
+Added ``orientation`` parameter for stem plots
+-----------------------------------
+When creating stem plots, you can now pass in an ``orientation`` argument to :func:`stem`.
+
+Currently, only ``vertical`` and ``horizontal`` orientations are supported,
+with ``horizontal`` being the default.
+
+Example
+```````
+stem(x, x, orientation='vertical')
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -2364,8 +2364,10 @@ def stem(self, *args, **kwargs):
 
         Call signatures::
 
-          stem(y, linefmt='b-', markerfmt='bo', basefmt='r-')
-          stem(x, y, linefmt='b-', markerfmt='bo', basefmt='r-')
+          stem(y, linefmt='b-', markerfmt='bo', basefmt='r-',
+              orientation = {'horizontal'|'vertical'})
+          stem(x, y, linefmt='b-', markerfmt='bo', basefmt='r-',
+              orientation = {'horizontal'|'vertical'})
 
         A stem plot plots vertical lines (using *linefmt*) at each *x*
         location from the baseline to *y*, and places a marker there
@@ -2374,17 +2376,39 @@ def stem(self, *args, **kwargs):
 
         If no *x* values are provided, the default is (0, 1, ..., len(y) - 1)
 
-        Return value is a tuple (*markerline*, *stemlines*,
-        *baseline*).
+        Optional parameters:
+        --------------------
+        linefmt : line format string
+            Format for the lines protruding from the baseline to the
+            stem markers.
+
+        markerfmt: marker format string
+            Format for the markers.
+
+        basefmt: line format string
+            Format for the baseline.
+
+        vertical: string, optional (horizontal)
+            If 'vertical', will produce a vertically-oriented stem plot,
+            else it will produce a horizontally-oriented stem plot.
+
+        bottom: num, optional (0)
+            The location of the base line.
+
+        label: string
+            Label for the stem container returned.
+
+        Returns
+        -------
+        The return value is ``(markerline, stemlines, baseline)``.
 
         .. seealso::
             This
             `document <http://www.mathworks.com/help/techdoc/ref/stem.html>`_
             for details.
 
-
-        **Example:**
-
+        Examples
+        --------
         .. plot:: mpl_examples/pylab_examples/stem_plot.py
         """
         remember_hold = self._hold
@@ -2420,22 +2444,42 @@ def stem(self, *args, **kwargs):
         except IndexError:
             basefmt = kwargs.pop('basefmt', 'r-')
 
+        # Check the orientation variable to see if the user
+        # wants a vertical or horizontal stem plot
+        orientation = kwargs.pop('orientation', 'horizontal')
+
+        if orientation not in ('horizontal', 'vertical'):
+            raise ValueError("'%s' is not a valid orientation" % orientation)
+
         bottom = kwargs.pop('bottom', None)
         label = kwargs.pop('label', None)
 
+        if orientation == 'vertical':
+            x, y = y, x
+
         markerline, = self.plot(x, y, markerfmt, label="_nolegend_")
 
         if bottom is None:
             bottom = 0
 
         stemlines = []
         for thisx, thisy in zip(x, y):
-            l, = self.plot([thisx, thisx], [bottom, thisy], linefmt,
-                           label="_nolegend_")
+            if orientation == 'vertical':
+                thisx, thisy = thisy, thisx
+                l, = self.plot([bottom, thisy], [thisx, thisx],  linefmt,
+                               label="_nolegend_")
+            else:
+                l, = self.plot([thisx, thisx], [bottom, thisy], linefmt,
+                               label="_nolegend_")
             stemlines.append(l)
 
-        baseline, = self.plot([np.amin(x), np.amax(x)], [bottom, bottom],
-                              basefmt, label="_nolegend_")
+        if orientation == 'vertical':
+            x, y = y, x
+            baseline, = self.plot([bottom, bottom], [np.amin(x), np.amax(x)],
+                                  basefmt, label="_nolegend_")
+        else:
+            baseline, = self.plot([np.amin(x), np.amax(x)], [bottom, bottom],
+                                  basefmt, label="_nolegend_")
 
         self.hold(remember_hold)
 

diff --git a/lib/matplotlib/tests/baseline_images/test_axes/stem_orientation.pdf b/lib/matplotlib/tests/baseline_images/test_axes/stem_orientation.pdf
diff --git a/lib/matplotlib/tests/baseline_images/test_axes/stem_orientation.png b/lib/matplotlib/tests/baseline_images/test_axes/stem_orientation.png