title: read subset of a single NetCDF file using slices of dimensions
body: <p>I have a very big <code>NetCDF</code> file.</p>
  
  <p>I tried to use the <code>dask.array</code> feature in python <code>xarray</code> module and specified the chunk size when I opened this data. It worked fine; however, when I tried to load the variables to memory using .load(), it was super slow.</p>
  
  <p>I wonder is there any option (in <code>xarray</code> or other python module) to read in subset of a <code>NetCDF</code> file by providing indices of dimensions (lat, lon)? That way I can directly apply functions to the subset file without using the <code>dask.array</code>.</p>