Ratio of the yields of $\Dzero$ and $\Dplus$ mesons measured as a function of $\pt$ in the small-$\qTPC$ (left column) and large-$\qTPC$ (right column) samples (see text for details) to that in the unbiased sample, in $\PbPb$ collisions at $\sqrtsNN=5.02 \TeV$ for the 10--30\% (top row) and 30--50\% (bottom row) centrality classes. Vertical error bars represent the statistical uncertainty, empty boxes the total systematic uncertainty.