1.1.1

Sorting algorithms may take tuples of keys/values (in fact, any Boost.Fusion sequence will do). One will have to explicitly specify the comparison functor in this case. Both host and device variants of the comparison functor should take 2n arguments, where n is the number of keys. The first n arguments correspond to the left set of keys, and the second n arguments correspond to the right set of keys. Here is an example that sorts values by a tuple of two keys:

vex::vector<int>    keys1(ctx, n);
vex::vector<float>  keys2(ctx, n);
vex::vector<double> vals (ctx, n);

struct {
    VEX_FUNCTION(device, bool(int, float, int, float),
            "return (prm1 == prm3) ? (prm2 < prm4) : (prm1 < prm3);"
            );
    bool operator()(int a1, float a2, int b1, float b2) const {
        return std::make_tuple(a1, a2) < std::tuple(b1, b2);
    }
} comp;

vex::sort_by_key(std::tie(keys1, keys2), vals, comp);