'Return the list *Tr*, where *Tr[r]* is the total count in
``heldout_fdist`` for all samples that occur *r*
times in ``base_fdist``.
:rtype: list(float)'

def _calculate_Tr(self):

    Tr = ([0.0] * (self._max_r + 1))
    for sample in self._heldout_fdist:
        r = self._base_fdist[sample]
        Tr[r] += self._heldout_fdist[sample]
    return Tr
