Well this is a way I have been advised to do. Previously, I have tried to use
apriori but the time and memory cost was too much to process half of items with
even two transactions.
thus I switched to use a heuristic way such as the one suggested in 
Is there anyway that I can use a small part, say 20x20, of the sparse matrix.
As ECJ does not have such an option I am trying to write a java code for that.
Am I in the right track?
 Ghosh et al. 2010, Mining Frequent Itemsets Using GA