17. A computer program product for performing association rule based data mining in an electronic data processing system, comprising: a non-transitory computer readable medium; computer program instructions, recorded on the computer readable medium, executable by a processor, for performing 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.
17. A computer program product for performing association rule based data mining in an electronic data processing system, comprising: a non-transitory computer readable medium; computer program instructions, recorded on the computer readable medium, executable by a processor, for performing 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. 18. The computer program product of claim 17 , wherein the step of counting each occurrence of each item or event in each data entry in the dataset comprises the step of: generating a count array comprising a first column including a plurality of identifiers, each identifier identifying an item or event in the dataset, and a second column comprising a plurality of counts, each count indicating a number of occurrences of an item or event identified by a corresponding identifier.