1. A computer-implemented method of determining a clustering metric, the method comprising: receiving, by a processor, a first set of transactions; receiving a second set of transactions; and for transaction i of the first set of transactions and transaction j of the second set of transactions: determining an intersection set comprising transactions that are neighbors of transaction i and transaction j; determining a union set comprising transactions that are neighbors of either transaction i or transaction j; computing a common linkage between transaction i and transaction j equal to the intersection set divided by the union set; determining a clustering metric based on the common linkage; and storing the clustering metric in memory.