issue_comments: 399315302

I'm not sure if my issue belongs in here, but I didn't want to create a new Issue (there are already 455 open ones).

I am experimenting with the new CFTimeIndex functionality (thanks heaps BTW! That was a mammoth effort if the PR thread is anything to go by).

I am trying to shift a time index as I need to align datasets to a common start point. So using the example code above,

```python da.time.get_index('time').shift(1,'D')

NotImplementedError Traceback (most recent call last) <ipython-input-71-db48b2fbb340> in <module>() ----> 1 da.time.get_index('time').shift(1,'D')

/g/data3/hh5/public/apps/miniconda3/envs/analysis27-18.04/lib/python2.7/site-packages/pandas/core/indexes/base.pyc in shift(self, periods, freq) 2627 """ 2628 raise NotImplementedError("Not supported for type %s" % -> 2629 type(self).name) 2630 2631 def argsort(self, args, *kwargs):

NotImplementedError: Not supported for type CFTimeIndex ``` Is this not implemented because it might require resampling?

I ask because this works: python times[0] + pd.Timedelta('365 days') cftime.DatetimeNoLeap(2, 1, 1, 0, 0, 0, 0, -1, 1)

I guess I am asking, if I want to shift a time index is the best (only?) way currently is to loop over all the individual elements of the index and add a time offset to each?