Methods and apparatus for detecting anomalies in electronic data are described. An example apparatus includes a signature generator to generate a signature of context information for electronic transactions and to query a memorybase of previously received electronic transactions to identify a first entity associated with a subset of historical transactions that are associated with the signature, a neighborhood generator to query the memorybase to generate a neighborhood for the first entity, a target category identifier to determine a target category value for entities included in the neighborhood, and an anomaly detector to determine a score for the first entity based on the target category value and to present an alert indicating that the first entity is anomalous based on the score.