title: Coordnate mapping on xarray dataset/datarray
body: <p>What is the recommended way to implemen coordinate mapping between xarray data?</p>
  <p>Here is my example/case:</p>
  <p>I have one DataArray <code>ndo3_1</code> with the following coordinates &quot;[time, <strong>plev</strong>, lat, lon]&quot;. Then I have another DataArray <code>h</code> with also &quot;[time, <strong>plev</strong>, lat, lon]&quot;.</p>
  <p>(<strong>plev</strong> is pressure_level and <strong>h</strong> is height)</p>
  <p>I need to convert &quot;ndo3_1[time, <strong>plev</strong>, lat, lon]&quot; to &quot;ndo3_2[time, <strong>h</strong>, lat, lon]&quot;. As you can see <code>h</code> is only a conversion matrix for <code>plev</code> as some models are easier to represent with equal pressures. However others are easier with height.</p>
  <p>Is it possible to achieve this?
  Which would be the recommended way?</p>
  <p>Note &quot;for&quot; loop in python would be really slow, the correct answer would use a functional approach using xarray operations.</p>