BUG : improved input clean up in Axes.{h|v}line

 - passing in a (N, 1) shaped array as input causes the zipping to
   generate an extra dimension
 - use squeeze to get rid of useless dimensions
 - use atleast_1d to make sure scalars remain 1D ((1, ) vs () shape)
 - closes matplotlib#2197

CHANGELOG

@@ -1,4 +1,7 @@
-2014-04-22 Added an example showing the difference between 
+2014-04-27 Improved input clean up in Axes.{h|v}lines
+	   Coerce input into a 1D ndarrays (after dealing with units).
+
+2014-04-22 Added an example showing the difference between
 	   interpolation = 'none' and interpolation = 'nearest' in
 	   `imshow()` when saving vector graphics files.
 
@@ -7,7 +10,7 @@
 
 2014-04-08 Fixed a bug in parasite_axes.py by making a list out
            of a generator at line 263.
-	   
+
 2014-02-25 In backend_qt4agg changed from using update -> repaint under
 	   windows.  See comment in source near `self._priv_update` for
 	   longer explaination.

lib/matplotlib/axes/_axes.py

@@ -955,18 +955,16 @@ def hlines(self, y, xmin, xmax, colors='k', linestyles='solid',
         if not iterable(xmax):
             xmax = [xmax]
 
-        y = np.asarray(y)
-        xmin = np.asarray(xmin)
-        xmax = np.asarray(xmax)
+        y = np.atleast_1d(np.asarray(y).squeeze())
+        xmin = np.atleast_1d(np.asarray(xmin).squeeze())
+        xmax = np.atleast_1d(np.asarray(xmax).squeeze())
 
-        if len(xmin) == 1:
-            xmin = np.resize(xmin, y.shape)
-        if len(xmax) == 1:
-            xmax = np.resize(xmax, y.shape)
+        if y.ndim != 1:
+            raise ValueError("y must be scalar or 1D")
 
-        if len(xmin) != len(y):
+        if xmin.shape != y.shape:
             raise ValueError('xmin and y are unequal sized sequences')
-        if len(xmax) != len(y):
+        if xmax.shape != y.shape:
             raise ValueError('xmax and y are unequal sized sequences')
 
         verts = [((thisxmin, thisy), (thisxmax, thisy))
@@ -1044,17 +1042,19 @@ def vlines(self, x, ymin, ymax, colors='k', linestyles='solid',
         if not iterable(ymax):
             ymax = [ymax]
 
-        x = np.asarray(x)
-        ymin = np.asarray(ymin)
-        ymax = np.asarray(ymax)
-        if len(ymin) == 1:
-            ymin = np.resize(ymin, x.shape)
-        if len(ymax) == 1:
-            ymax = np.resize(ymax, x.shape)
+        x = np.atleast_1d(np.asarray(x).squeeze())
+        ymin = np.atleast_1d(np.asarray(ymin).squeeze())
+        ymax = np.atleast_1d(np.asarray(ymax).squeeze())
 
-        if len(ymin) != len(x):
+        if x.ndim != 1:
+            print(x)
+            print(ymin)
+            print(ymax)
+            raise ValueError('x input must be scalar or 1 dimensional')
+
+        if ymin.shape != x.shape:
             raise ValueError('ymin and x are unequal sized sequences')
-        if len(ymax) != len(x):
+        if ymax.shape != x.shape:
             raise ValueError('ymax and x are unequal sized sequences')
 
         Y = np.array([ymin, ymax]).T