davidr, #kdtree and ball trees seem cool, but require full knowledge of the thing I'm searching for. What if it's 7 dimensional and I only know 4 of the values?
I feel like a "parallel kd tree" with a separate binary index on each dimension would work better here.
Reduce depth. Allow unspecified values. It'd also be a snap to create and search each dim in parallel.
This must already exist...