While I was studying the formulation of market basket analysis problem in the book Elements of Statistical Learning in the chapter unsupervised learning, I came through the following statement:
The Apriori algorithm requires only one pass over the data for each value of T ( K ), which is crucial since we assume the data cannot be fitted into a computer’s main memory. If the data are sufficiently sparse (or if the threshold t is high enough), then the process will terminate in reasonable time even for huge data sets.
where, T(K) is the support of item-set K.
The Apriori algorithm requires only one pass over the data for each value of T ( K )
is not making any sense to me. Since this algorithm involves many repetition then why are they talking about "only one pass"? What does mean by "pass" here? How is T(k) "crucial" here?
And what does mean by the phrase ?
data are sufficiently sparse