Avoid unneeded copies from flatten().

anntzer · anntzer · commit 1ebf1c3cb5f8 · 2019-02-07T22:36:07.000+01:00
flatten() always returns a new copy, but nearly all places that use
flatten() in the codebase don't need to pay that cost; the only place
that needed it did an additional copy.  Fix them.

As a replacement, there's ravel(), which only makes a copy if the input
is not C-contiguous to start with, and reshape(..., -1) which never
makes a copy (as long as the input is already an ndarray), so prefer the
latter.

Note that in the changed snippet in mplot3d, the AttributeError would
never be raised, as x/y/z are converted to arrays and thus always have a
flatten() method.
diff --git a/lib/matplotlib/transforms.py b/lib/matplotlib/transforms.py
@@ -282,7 +282,7 @@ def __array__(self, *args, **kwargs):
 
     def is_unit(self):
         """Return whether this is the unit box (from (0, 0) to (1, 1))."""
-        return list(self.get_points().flatten()) == [0., 0., 1., 1.]
+        return self.get_points().tolist() == [[0., 0.], [1., 1.]]
 
     @property
     def x0(self):
@@ -413,13 +413,13 @@ def size(self):
     @property
     def bounds(self):
         """Return (:attr:`x0`, :attr:`y0`, :attr:`width`, :attr:`height`)."""
-        x0, y0, x1, y1 = self.get_points().flatten()
+        (x0, y0), (x1, y1) = self.get_points()
         return (x0, y0, x1 - x0, y1 - y0)
 
     @property
     def extents(self):
         """Return (:attr:`x0`, :attr:`y0`, :attr:`x1`, :attr:`y1`)."""
-        return self.get_points().flatten().copy()
+        return self.get_points().flatten()  # flatten returns a copy.
 
     def get_points(self):
         raise NotImplementedError
@@ -1758,10 +1758,10 @@ def is_separable(self):
 
     def to_values(self):
         """
-        Return the values of the matrix as a sequence (a,b,c,d,e,f)
+        Return the values of the matrix as an ``(a, b, c, d, e, f)`` tuple.
         """
         mtx = self.get_matrix()
-        return tuple(mtx[:2].swapaxes(0, 1).flatten())
+        return tuple(mtx[:2].swapaxes(0, 1).flat)
 
     @staticmethod
     def matrix_from_values(a, b, c, d, e, f):
diff --git a/lib/mpl_toolkits/mplot3d/axes3d.py b/lib/mpl_toolkits/mplot3d/axes3d.py
@@ -490,22 +490,16 @@ def autoscale(self, enable=True, axis='both', tight=None):
                                          scalez=scalez)
 
     def auto_scale_xyz(self, X, Y, Z=None, had_data=None):
-        x, y, z = map(np.asarray, (X, Y, Z))
-        try:
-            x, y = x.flatten(), y.flatten()
-            if Z is not None:
-                z = z.flatten()
-        except AttributeError:
-            raise
-
-        # This updates the bounding boxes as to keep a record as
-        # to what the minimum sized rectangular volume holds the
-        # data.
-        self.xy_dataLim.update_from_data_xy(np.array([x, y]).T, not had_data)
-        if z is not None:
+        # This updates the bounding boxes as to keep a record as to what the
+        # minimum sized rectangular volume holds the data.
+        X = np.reshape(X, -1)
+        Y = np.reshape(Y, -1)
+        self.xy_dataLim.update_from_data_xy(
+            np.column_stack([X, Y]), not had_data)
+        if Z is not None:
+            Z = np.reshape(Z, -1)
             self.zz_dataLim.update_from_data_xy(
-                np.array([z, z]).T, not had_data)
-
+                np.column_stack([Z, Z]), not had_data)
         # Let autoscale_view figure out how to use this data.
         self.autoscale_view()
 
