Abstract: Provided is a method for performing similarity search. The method comprises generating a reverse index from entity data, wherein the reverse index comprises entries where each entry has a key corresponding to a characteristic value of an entity and a value containing a list of entity identifiers in which the characteristic value appeared and a count of entities in which the characteristic value appeared. The method further comprises eliminating or reducing the list of entity identifiers for entries where the count exceeds a predetermined threshold (e.g., loss-permitted). Using loss-permitted reverse indexing, the system enables efficient storage/retrieval of high-dimensional data, allowing real-time similarity calculations for recommendation engines, image search, anomaly detection, and fraud detection.