Dear @lilina ,
Meanwhile, I noticed there had been a somewhat related discussion in another forum post. In particular, you can always manually call numpy.asarray on any RVec for a fast, zero-copy conversion as discussed here. In that case the user wanted all the floats from all the events concatenated in a single flattened numpy array, which is not your case as I understand it. But, if it makes the workflow easier, you could think about running the mask np_nosmear["set"]==1 on the outer numpy array, then using numpy.asarray on the resulting RVecs and pass the result to plt.scatter.
Let me know if this helps,
Cheers,
Vincenzo