Reading about association rules mining made me somehow confused. I am wondering if this is possible that in a transaction, an item occurs more than once? Considering the following database as a reference:

Transaction id  Items
         t1     {1,4,1}
         t2     {2}
         t3     {1,2,1}
         t4     {2,2}
         t5     {1, 2, 3, 5}

1 Answer 1


I don't think so. Are your item sets destined for the apriori algorithm? The apriori algorithm is based on the presence or absence of items in, say, a shopping basket. It doesn't care about how many items you buy of a particular kind. Alternatively, you could treat different quantities as different items -- so that a six-pack of beer is different from a two-four.

  • $\begingroup$ Yes, I am referring to apriori algorithm. what do you mean two-four? in addition, how can I tell the algorithm that these 6 items are actually 6 instances of a same type? $\endgroup$
    – lonesome
    Commented Nov 8, 2015 at 4:34
  • $\begingroup$ A two-four is a pack of 24 bottles of beer. It's a Canadian thing. The apriori algorithm uses a big transaction matrix - items in columns, transactions in rows, with a 0 or 1 in each cell. It can't deal with "6 items of the same type", so you would have to clean the data first: "Joe bought beer and chips"; "Jane bought beer and beef". There may be a different algorithm out there that handles multiples. Why do you want to make that distinction? i.e. buying 6 beers is associated with buying 2 large pizzas? But buying 5 beers is associated with .... buying fish sticks. $\endgroup$
    – Placidia
    Commented Nov 8, 2015 at 4:42
  • $\begingroup$ the distinction is due to the fact that , in my mind, buying 6 of a soft drink with something would have more weight compare to buying , say, 2 of the same soft drink with some other item. In other words, it would be more associated to the first item compare to the second item. does that make any sense? I hope it does. $\endgroup$
    – lonesome
    Commented Nov 8, 2015 at 10:55
  • $\begingroup$ If you want to relate quantity to presence - as in the more diapers you buy the more likely you are to buy baby food - then you are into logistic regression models. However these only work for one response at a time. For groceries, the quantity is a function of how many people you are feeding. Lots of hot dogs go with lots of hot dog buns. A large quantity might indicate that someone is holding a party, or in a hardware situation, that the purchaser is a builder. You would need a lot of domain specific knowledge to build a model like that. apriori isn't that smart. $\endgroup$
    – Placidia
    Commented Nov 8, 2015 at 14:28
  • $\begingroup$ Actually my real model is not about shopping list but it can be seen as what I explained. In this case, that apriori is a little dumb for such functionalities, what is your suggestion? I mean in terms of statistic modeling. $\endgroup$
    – lonesome
    Commented Nov 9, 2015 at 1:57

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