code: def mask_average(dset,mask):
      '''Returns average of voxels in ``dset`` within non-zero voxels of ``mask``'''
      o = nl.run(['3dmaskave','-q','-mask',mask,dset])
      if o:
          return float(o.output.split()[-1]f mask_average(dset,mask):
      '''Returns average of voxels in ``dset`` within non-zero voxels of ``mask``'''
      o = nl.run(['3dmaskave','-q','-mask',mask,dset])
      if o:
          return float(o.output.split()[-1])
docs: Returns average of voxels in ``dset`` within non-zero voxels of ``mask``