In one embodiment, an apparatus comprises a storage device and a processor. The storage
device stores a feature vector index, wherein the feature vector index comprises a sparse-
array data structure representing a feature space for a set of labeled feature vectors, wherein
the set of labeled feature vectors are assigned to a plurality of classes. The processor is to:
receive a query corresponding to a target feature vector; access, via the storage device, a
first portion of the feature vector index, wherein the first portion of the feature vector index …