A device (100) for and method of determining clusters of sequences of instances of a first type of data for compacting a data set comprising sequences of instances of the first type of data is provided. Also a method of compacting a data set, a method of transmitting compacted data and a computer program product are provided. In a sequence clustering unit (110) of the device, sequences of a first set of data are clustered on basis of conditional probabilities. Each unique sequence of the first set of data is associated with one or more conditional probabilities that an instance of the second set of data has a specific value given the unique sequence. In the clustering a significant part of the mutual information between the first set of data and the second set of data is maintained.