title: Is there any easy way to compute seasonal mean with xarray?
body: <p>A lot of monthly NetCDF files contains all months in many years (for example, from Jan1948 to Dec2018).</p>
  
  <p>How to use Xarray to compute the seasonal average of each year conveniently?</p>
  
  <p>There are <a href="http://xarray.pydata.org/en/stable/examples/monthly-means.html" rel="nofollow noreferrer">examples</a> using <code>GroupBy</code> to calculate seasonal average, but it seems to group all the months spanning many years to 4 groups, which can't give the seasonal average of every year.</p>