apriori.rb - la ruby presentation
DESCRIPTION
Nate Murray's talk on Apriori.rb - A ruby gem/wrapper around Christian Borgelt’s apriori.c software for finding frequently purchased itemsetsTRANSCRIPT
AprioriA Ruby wrapper for
Christian Borgelt’s implementationof Agrawal et al.’s algorithm
what does it do?
picture of a grocery store
overview
overview
• Find regularities in shopping behavior
overview
• Find regularities in shopping behavior
• Market Basket Analysis
overview
• Find regularities in shopping behavior
• Market Basket Analysis
• Sets of products
suggest items to a customer
association rules
association rules
association rules
“A customer who buys apples buys cheese with 30% certainty”
association rules
“A customer who buys apples buys cheese with 30% certainty”
Confidence
why would we want to do this?
picture of “buy this too”
Example
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
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✓ ✓
Item
s
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
Customers
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
purchased
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
problem:
too many possible rules
solution:
Don’t look at all the rules(which is how Apriori works)
term:
Itemset:a combination of one or more items
examples of itemsets
examples of itemsets
examples of itemsets
examples of itemsets
examples of itemsets
Step 1) Build a prefix tree
prefix
prefix
prefix
prefix
prefix
prefix
Step 2) Prune statistically insignificant rules
statistically significant
term:
Support:the percentage of transactions that a rule/itemset can be applied to
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
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✓ ✓
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✓ ✓
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✓ ✓
3/5
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
3/5 = 60%
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
3/5 = 60%
Support
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
2/5
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
2/5 = 40%
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
2/5 = 40%
Support
support of:
= 40% support of:
The key optimization:
= 40% support of:
= 40% support of:
support of:
= 40% support of:
support of:
= 40% support of:
support of:
+
= 40% support of:
support of:
+
= 40% support of:
support of:
+ <= 40%
Step 3) Find “good” rules
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
need a way to calculate “goodness”
term:
term:
Confidence:number of cases in which the rule is correct relative to the number of cases in which it is applicable
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
->
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
->
2/2
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
->
2/2 = 100%
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
->
2/2 = 100%
Confidence
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
->
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
->
1/3
✓ ✓✓ ✓✓ ✓ ✓✓ ✓
✓ ✓
->
1/3 = 33%
intermission
Apriori(in ruby)
code example
available today
gem install apriori
requires: rubygems >= 1.2.0
gem update --system
AprioriA Ruby wrapper for
Christian Borgelt’s implementationof Agrawal et al.’s algorithm
AprioriA Ruby wrapper for
Christian Borgelt’s implementationof Agrawal et al.’s algorithm