Data processing apparatuses and data processing methods are provided. The data processing apparatus includes a storage unit, an interface, and a processor. The storage unit stores a first key-value set including a plurality of first key-value pairs. Each of the first key-value pairs has a first key and a first value. The interface receives an instruction regarding a set operation and a function. The processor generates a plurality of second keys by applying the set operation to the first keys. Each of the second keys includes at least one of the first keys. The processor generates a second value for each of the second keys by applying the function to at least one datum corresponding to the at least one first key comprised in the second key. Each second key and the corresponding second value form a second key-value pair and the second key-value pairs form a second key-value set.