In this tutorial, we will try to answer the following questions;
- What are the Apriori candidate’s generations?
- What is self-joining?
- what is the Apriori pruning principle?
Apriori Candidates generation:
Candidates can be generated by the self joining and Apriori pruning principles.
Step 1:
self-joining
Example of self-joining
V W X Y ZX={V W X, V W Y, V X Y, V X Z, W X Y}Self-joining = X * XV W X Y from V W X and V W YV X Y Z from V X Y and V X Z
So frequent candidates are V W X Y and V X Y Z
Step 2:
Apriori pruning principle:
Example of Apriori pruning principle
V W X Y ZX={V W X, V W Y, V X Y, V X Z, W X Y} According to Apriori Pruning principle V X Y Z is removed because V Y Z is not in X.
So frequent candidate is V W X Y
Apriori Candidates generation
Candidates can be generated by the self joining and Apriori pruning principles.
Step 1:
Self-joining of Apriori Candidates
Example of self-joining
A1 B1 C1 D1 E1
C1={A1 B1 C1, A1 B1 D1, A1 C1 D1, A1 C1 E1, B1 C1 D1}
Self-joining = C1 * C1A1 B1 C1 D1 from A1 B1 C1 and A1 B1 D1A1 C1 D1 E1 from A1 C1 D1 and A1 C1 E1
So frequent candidates are A1 B1 C1 D1 and A1 C1 D1 E1
Step 2:
Apriori pruning principle
Example of Apriori pruning principle
A1 B1 C1 D1 E1C1={A1 B1 C1, A1 B1 D1, A1 C1 D1, A1 C1 E1, B1 C1 D1} According to Apriori Pruning principle A1 C1 D1 E1 is remoA1ed because A1 D1 E1 is not in C1.
So frequent candidate is A1 B1 C1 D1.
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