docs: def plot_average(sdat, lovs):
      """Plot time averaged profiles.
  
      Args:
          sdat (:class:`~stagpy.stagyydata.StagyyData`): a StagyyData instance.
          lovs (nested list of str): nested list of profile names such as
              the one produced by :func:`stagpy.misc.list_of_vars`.
  
      Other Parameters:
          conf.core.snapshots: the slice of snapshots.
          conf.conf.timesteps: the slice of timesteps.
      """
      steps_iter = iter(sdat.walk.filter(rprof=True))
      try:
          step = next(steps_iter)
      except StopIteration:
          return
  
      sovs = misc.set_of_vars(lovs)
  
      istart = step.istep
      nprofs = 1
      rprof_averaged = {}
      rads = {}
      metas = {}
  
      # assume constant z spacing for the moment
      for rvar in sovs:
          rprof_averaged[rvar], rad, metas[rvar] = get_rprof(step, rvar)
          if rad is not None:
              rads[rvar] = rad
  
      for step in steps_iter:
          nprofs += 1
          for rvar in sovs:
              rprof_averaged[rvar] += get_rprof(step, rvar)[0]
  
      ilast = step.istep
      for rvar in sovs:
          rprof_averaged[rvar] /= nprofs
      rcmb, rsurf = misc.get_rbounds(step)
      rprof_averaged['bounds'] = (step.sdat.scale(rcmb, 'm')[0],
                                  step.sdat.scale(rsurf, 'm')[0])
      rprof_averaged['r'] = get_rprof(step, 'r')[0] + rprof_averaged['bounds'][0]
  
      stepstr = '{}_{}'.format(istart, ilast)
  
      _plot_rprof_list(sdat, lovs, rprof_averaged, metas, stepstr, rads)