Yes, if they’re just data, you can do that.
Otherwise, you need to sort and select (and maybe interpolate if you really want to go to town), as @sakrejda was outlining.
We probably should have a quantile function for data and generated quantities. It doesn’t make much sense in the model block as the sorting itself is going to act kind of like a step function (at some threshold, a different variable contributes, but that threshold’s not itself contributing to derivatives, but set by another element).