Apriori Algorithm for Generating Frequent Itemsets

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Apriori Algorithm is used in finding frequent itemsets. Identifying associations between items in a dataset of transactions can be useful in various data mining tasks. For example, a supermarket can make better shelf arrangement if they know which items are purchased together frequently. The challenge is that given a dataset D having T transactions each with n number of attributes, how to find itemsets that appear frequently in D? This can be trivially solved by generating all possible itemsets (and checking each of the candidate itemset against support threshold.) which is computationally expensive. Apriori algorithm effectively eliminates majority of itemsets without counting their suppor
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Devji Chhanga

I teach computer science at university of Kutch since 2011, Kutch is the western most district of India. At iDevji, I share tech stories that excite me. You will love reading the blog if you too believe in the disruptive power of technology. Some stories are purely technical while others can involve empathetical approach to problem solving using technology.

2 Comments

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  • Here is an implementation to get all subsets of a set in Scheme:

    (define (subsets s)
    (if (null? s)
    (list ‘())
    (let ((rest (subsets (cdr s))))
    (append rest (map (lambda (x) (cons (car s) x)) rest)))))

    A very nice and clear explanation. I will try to implement the algorithm in Scheme.

    I have a question:
    What is the mathematical reason of dividing by “total transactions” while calculating the support value?

    • In this example only absolute support value is used, that is if an itemset appears 3 times support is stated as 3. But if you want to generalize support calculation, you need to use this formula. Obviously, denominator is total number of TXNs because we want to figure out how frequent an itemset is!

Devji Chhanga

I teach computer science at university of Kutch since 2011, Kutch is the western most district of India. At iDevji, I share tech stories that excite me. You will love reading the blog if you too believe in the disruptive power of technology. Some stories are purely technical while others can involve empathetical approach to problem solving using technology.

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