Add whats_new and update docstring

lkilcher · lkilcher · commit 65becd1f6bfa · 2017-09-27T13:39:35.000-06:00
diff --git a/doc/users/next_whats_new/colormap_utils.rst b/doc/users/next_whats_new/colormap_utils.rst
@@ -0,0 +1,56 @@
+Colormap Utilities
+------------------
+
+Tools for joining, truncating, and resampling colormaps have been added. This grew out of https://gist.github.com/denis-bz/8052855, and http://stackoverflow.com/a/18926541/2121597.
+
+
+Joining Colormaps
+~~~~~~~~~~~~~~~~~
+
+This includes the :func:`~matplotlib.colors.join_colormaps` function::
+
+  import matplotlib.pyplat as plt
+  from matplotlib.colors import join_colormaps
+
+  viridis = plt.get_cmap('viridis', 128)
+  plasma = plt.get_cmap('plasma_r', 64)
+  jet = plt.get_cmap('jet', 64)
+  
+  joined_cmap = join_colormaps((viridis, plasma, jet))
+
+This functionality has also been incorporated into the :meth:`~matplotlib.colors.colormap.join` and `~matplotlib.colors.colormap.__add__` methods, so that you can do things like::
+
+  plasma_jet = plasma.join(jet)
+
+  joined_cmap = viridis + plasma + jet  # Same as `join_colormaps` function call above
+
+Truncating and resampling colormaps
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+  
+A :meth:`~matplotlib.colors.colormap.truncate` method has also been added::
+
+  sub_viridis = viridis.truncate(0.3, 0.8)
+
+This gives a new colormap that goes from 30% to 80% of viridis. This functionality has also been implemented in the `~matplotlib.colors.colormap.__getitem__` method, so that the same colormap can be created by::
+
+  sub_viridis = viridis[0.3:0.8]
+
+The `~matplotlib.colors.colormap.__getitem__` method also supports a range of other 'advanced indexing' options, including integer slice indexing::
+
+  sub_viridis2 = viridis[10:90:2]
+
+integer list indexing, which may be particularly useful for creating discrete (low-N) colormaps::
+
+  sub_viridis3 = viridis[[4, 35, 59, 90, 110]]
+
+and `numpy.mgrid` style complex indexing::
+
+  sub_viridis4 = viridis[0.2:0.4:64j]
+
+See the `~matplotlib.colors.colormap.__getitem__` documentation for more details and examples of how to use these advanced indexing options.
+
+Together, the join and truncate/resample methods allow the user to quickly construct new colormaps from existing ones::
+
+  new_cm = viridis[0.5:] + plasma[:0.3] + jet[0.2:0.5:64j]
+
+I doubt this colormap will ever be useful to someone, but hopefully it gives you the idea.
diff --git a/lib/matplotlib/colors.py b/lib/matplotlib/colors.py
@@ -761,7 +761,6 @@ def truncate(self, minval=0.0, maxval=1.0, name=None, N=None):
     def __getitem__(self, item):
         """Advanced indexing for colorbars.
 
-
         Examples
         --------
         import matplotlib.pyplat as plt
@@ -780,7 +779,7 @@ def __getitem__(self, item):
 
         # Same as above, but specify the number of points
         # using `np.mgrid` complex-indexing:
-        new_cm = cmap[0.2:-0.4:1j * 64]
+        new_cm = cmap[0.2:-0.4:64j]
 
         # ### Int-style indexing
         # for int-style indexing, the values must be in [0, self.N]
@@ -793,7 +792,7 @@ def __getitem__(self, item):
         new_cm = cmap[12:-28:4]
 
         # And so is `np.mgrid` complex-indexing (same as above)
-        new_cm = cmap[12:-28:1j * 22]
+        new_cm = cmap[12:-28:22j]
 
         # ### Array/list-style indexing
         # In this case, you specify specific points in the colormap
