Transactional dataset

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Hi all, How can I import in RapidMiner a transacional dataset like this:

item1 item2 item3 item4
item2 item3
item5 item6 item7 item8
...

Because if I use the import wizard it looks only at the number of items(columns) present in the first 100 rows, but if there after more long transaction it lost them. How can manage this transactional dataset. I need it to use the classical fpgrowth algorithm and rule generation... Thanks to all