title: Substitute dataset coordinates in xarray (Python)
body: <p>I have a dataset stored in NetCDF4 format that consists of <code>Intensity</code> values with 3 dimensions: <code>Loop</code>, <code>Delay</code> and <code>Wavelength</code>. I named my coordinates the same as the dimensions (I don't know if it's good or bad...)</p>
  <p>I'm using <strong>xarray</strong> (formerly xray) in Python to load the dataset:</p>
  <pre><code>import xarray as xr
  ds = xr.open_dataset('test_data.netcdf4')
  </code></pre>
  <p>Now I want to manipulate the data while keeping track of the original data. For instance, I would:</p>
  <ol>
  <li><p>Apply an offset to the <code>Delay</code> coordinates and keep the original <code>Delay</code> dataarray untouched. This seems to be done with:</p>
  <p><code>ds_ = ds.assign_coords(Delay_corr=ds_.Delay.copy(deep=True) + 25)</code></p>
  </li>
  <li><p>Substitute the coordinates <code>Delay</code> for <code>Delay_corr</code> for all relevant dataarrays in the dataset. However, I have no clue how to do this and I didn't find anything in the documentation.</p>
  </li>
  </ol>
  <p>Would anybody know how to perform item #2?</p>
  <p>To download the NetCDF4 file with test data:
  <a href="http://1drv.ms/1QHQTRy" rel="noreferrer">http://1drv.ms/1QHQTRy</a></p>