apriori algorithm example

August 19, 2017

apriori algorithm example

Examples

1) Given the following data , apply Apriori algorithm. Min support = 50% and confidence = 70%
Database D.

TID	Sup
100	1 3 4
200	2 3 5
300	1 2 3 5
400	2 5

SOLUTION

Support (S) = (50/100) * 4

where min support = 50% and no of rows in database D is 4

Therefore S=2

Step 1 : Scan database D for count of each candidate which are present in "Items" column in the question. The candidate list is {1,2,3,4,5} and find the support. here support(S) = 2.

C₁=

Itemset	Sup
{1}	2
{2}	3
{3}	3
{4}	1
{5}	3

Step 2 : Compare candidate support count with minimum support count (i.e 50% in our case)

L₁=

Itemset	Sup
{1}	2
{2}	3
{3}	3
{5}	3

Step 3 : Generate candidate C₂ from L₁
C₂ =

Itemset
{1 2}
{1 3}
{1 5}
{2 3}
{2 5}
{3 5}

Step 4 : Scan database D for count of each candidate in C₂ and find the support

C₂ =

Itemset	Sup
{1 2}	1
{1 3}	2
{1 5}	1
{2 3}	2
{2 5}	3
{3 5}	2

Step 5 : Compare candidate (C₂) support count with the minimum support count

L₂=

Itemset	Sup
{1 3}	2
{2 3}	2
{2 5}	3
{3 5}	2

Step 6 : generate candidate C₃from L₂

C₃ =

Itemset
{1 3 5}
{2 3 5}
{1 2 3}

Step 7 :Scan database D for count of each candidate in C₃

C₃ =

Itemset	Sup
{1 3 5}	1
{2 3 5}	2
{1 2 3}	1

Step 8 : Compare candidate (C₃) support count with the minimum support count

L₃=

Itemset	Sup
{2 3 5}	2

Step 9 : So data contain the frequent itemset (2,3,5)

Therefore the association rule that can be generated from L₃ are as shown below with the support and confidence .

Association rule	Support	Confidence	Confidence %
2^3 => 5	2	2/2 = 1	100%
3^5 => 2	2	2/2 = 1	100%
2^5 => 3	2	2/3 = 0.66	66%
2 => 3^5	2	2/3 = 0.66	66%
3 => 2^5	2	2/3 = 0.66	66%
5 => 2^3	2	2/3 = 0.66	66%

If the minimum confidence threshold is 70% (Given), then only the first and second rules above are output, since these are the only ones generated that are strong

Final rules are :

Rule 1 : 2^3=>5 and Rule 2 : 3^5=>2

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NOTE : FOR ANY QUERIES COMMENT YOUR DOUBTS BELOW IN COMMENT BOX.
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FOR MORE EXAMPLE ON APRIORI ALGORITHM VISIT YOUTUBE LINK IN THE DESCRIPTION BELOW :

https://www.youtube.com/watch?v=JZepOmvB514