1. A computer-implemented method of performing association rule based data mining in an electronic data processing system comprising the steps of: providing a dataset comprising a plurality of data entries, each data entry comprising information relating to an item or event; counting each occurrence of each item or event in each data entry in the dataset; generating, for each item or event, a compilation of data entries that include each item or event; determining frequent itemsets, each itemset including a plurality of items or events in the dataset; generating a support count for each frequent itemset by determining support counts for a plurality of itemsets in a range of sizes of itemsets in one pass, wherein the support counts of candidates within a particular size range are determined by generating the candidates and arranging them in a lattice; and generating and compressing a vertical representation during the one pass.