Algorithms so far: compute exact collection of frequent itemsets of size k in k passes

 A-Priori, PCY, Multistage, Multihash

Many applications where it is not essential to discover every frequent itemset.

The algorithms for frequent itemsets discussed so far use one pass for each size of item set we investigate.

If main memory is too small to hold the data and the space needed to

count frequent itemsets of one size, there does not seem to be any way to

avoid k passes to compute the exact collection of frequent itemsets.

However, there are many applications where it is not essential to discover every frequent itemset.