Data Mining Association Analysis Introduction to Data Mining by Tan, Steinbach, Kumar ©...

Data Mining Association Analysis

Introduction to Data Miningby

Tan, Steinbach, Kumar

© Tan,Steinbach, Kumar Introduction to Data Mining 4/18/2004 1


Association Rule Mining

Given a set of transactions, find rules that will predict the occurrence of an item based on the occurrences of other items in the transaction

Market-Basket transactions

TID Items

1 Bread, Milk

2 Bread, Diaper, Beer, Eggs

3 Milk, Diaper, Beer, Coke

4 Bread, Milk, Diaper, Beer

5 Bread, Milk, Diaper, Coke

Example of Association Rules

{Diaper} {Beer},{Milk, Bread} {Eggs,Coke},{Beer, Bread} {Milk},

Implication means co-occurrence, not causality!


Definition: Frequent Itemset

Itemset– A collection of one or more items

Example: {Milk, Bread, Diaper}

– k-itemset An itemset that contains k items

Support count ()– Frequency of occurrence of an itemset

– E.g. ({Milk, Bread,Diaper}) = 2

Support– Fraction of transactions that contain an

itemset

– E.g. s({Milk, Bread, Diaper}) = 2/5

Frequent Itemset– An itemset whose support is greater

than or equal to a minsup threshold

TID Items

1 Bread, Milk






Definition: Association Rule

Example:Beer}Diaper,Milk{

4.052

|T|)BeerDiaper,,Milk(

s

67.032

)Diaper,Milk()BeerDiaper,Milk,(

c

Association Rule– An implication expression of the form

X Y, where X and Y are itemsets

– Example: {Milk, Diaper} {Beer}

Rule Evaluation Metrics– Support (s)

Fraction of transactions that contain both X and Y

– Confidence (c) Measures how often items in Y

appear in transactions thatcontain X

TID Items

1 Bread, Milk






Association Rule Mining Task

Given a set of transactions T, the goal of association rule mining is to find all rules having – support ≥ minsup threshold

– confidence ≥ minconf threshold

Brute-force approach:– List all possible association rules

– Compute the support and confidence for each rule

– Prune rules that fail the minsup and minconf thresholds

Computationally prohibitive!


Mining Association Rules

Example of Rules:

{Milk,Diaper} {Beer} (s=0.4, c=0.67){Milk,Beer} {Diaper} (s=0.4, c=1.0){Diaper,Beer} {Milk} (s=0.4, c=0.67){Beer} {Milk,Diaper} (s=0.4, c=0.67) {Diaper} {Milk,Beer} (s=0.4, c=0.5) {Milk} {Diaper,Beer} (s=0.4, c=0.5)

TID Items

1 Bread, Milk





Observations:

• All the above rules are binary partitions of the same itemset: {Milk, Diaper, Beer}

• Rules originating from the same itemset have identical support but can have different confidence

• Thus, we may decouple the support and confidence requirements


Mining Association Rules

Two-step approach: 1. Frequent Itemset Generation

– Generate all itemsets whose support minsup

2. Rule Generation– Generate high confidence rules from each frequent itemset,

where each rule is a binary partitioning of a frequent itemset

Frequent itemset generation is still computationally expensive


Frequent Itemset Generation

null

AB AC AD AE BC BD BE CD CE DE

A B C D E

ABC ABD ABE ACD ACE ADE BCD BCE BDE CDE

ABCD ABCE ABDE ACDE BCDE

ABCDE

Given d items, there are 2d possible candidate itemsets


Frequent Itemset Generation

Brute-force approach: – Each itemset in the lattice is a candidate frequent itemset

– Count the support of each candidate by scanning the database

– Match each transaction against every candidate

– Complexity ~ O(NMw) => Expensive since M = 2d !!!

TID Items 1 Bread, Milk 2 Bread, Diaper, Beer, Eggs 3 Milk, Diaper, Beer, Coke 4 Bread, Milk, Diaper, Beer 5 Bread, Milk, Diaper, Coke

N

Transactions List ofCandidates

M

w


Computational Complexity

Given d unique items:– Total number of itemsets = 2d

– Total number of possible association rules:

123 1

1

1 1

dd

d

k

kd

j j

kd

k

dR

If d=6, R = 602 rules


Frequent Itemset Generation Strategies

Reduce the number of candidates (M)– Complete search: M=2d

– Use pruning techniques to reduce M

Reduce the number of transactions (N)– Reduce size of N as the size of itemset increases– Used by DHP and vertical-based mining algorithms

Reduce the number of comparisons (NM)– Use efficient data structures to store the candidates or

transactions– No need to match every candidate against every

transaction


Reducing Number of Candidates

Apriori principle:– If an itemset is frequent, then all of its subsets must also

be frequent

Apriori principle holds due to the following property of the support measure:

– Support of an itemset never exceeds the support of its subsets

– This is known as the anti-monotone property of support

)()()(:, YsXsYXYX


Found to be Infrequent

null


A B C D E



ABCDE

Illustrating Apriori Principle

null


A B C D E



ABCDEPruned supersets


Illustrating Apriori Principle

Item CountBread 4Coke 2Milk 4Beer 3Diaper 4Eggs 1

Itemset Count{Bread,Milk} 3{Bread,Beer} 2{Bread,Diaper} 3{Milk,Beer} 2{Milk,Diaper} 3{Beer,Diaper} 3

Itemset Count {Bread,Milk,Diaper} 3

Items (1-itemsets)

Pairs (2-itemsets)

(No need to generatecandidates involving Cokeor Eggs)

Triplets (3-itemsets)Minimum Support = 3

If every subset is considered, 6C1 + 6C2 + 6C3 = 41

With support-based pruning,6 + 6 + 1 = 13


Apriori Algorithm

Method:

– Let k=1– Generate frequent itemsets of length 1– Repeat until no new frequent itemsets are identified

Generate length (k+1) candidate itemsets from length k frequent itemsets

Prune candidate itemsets containing subsets of length k that are infrequent

Count the support of each candidate by scanning the DB Eliminate candidates that are infrequent, leaving only those

that are frequent


Reducing Number of Comparisons

Candidate counting:– Scan the database of transactions to determine the

support of each candidate itemset– To reduce the number of comparisons, store the

candidates in a hash structure Instead of matching each transaction against every candidate, match it against candidates contained in the hashed buckets

TID Items 1 Bread, Milk 2 Bread, Diaper, Beer, Eggs 3 Milk, Diaper, Beer, Coke 4 Bread, Milk, Diaper, Beer 5 Bread, Milk, Diaper, Coke

N

Transactions Hash Structure

k

Buckets


Generate Hash Tree

2 3 45 6 7

1 4 51 3 6

1 2 44 5 7 1 2 5

4 5 81 5 9

3 4 5 3 5 63 5 76 8 9

3 6 73 6 8

1,4,7

2,5,8

3,6,9Hash function

Suppose you have 15 candidate itemsets of length 3:

{1 4 5}, {1 2 4}, {4 5 7}, {1 2 5}, {4 5 8}, {1 5 9}, {1 3 6}, {2 3 4}, {5 6 7}, {3 4 5}, {3 5 6}, {3 5 7}, {6 8 9}, {3 6 7}, {3 6 8}

You need:

• Hash function

• Max leaf size: max number of itemsets stored in a leaf node (if number of candidate itemsets exceeds max leaf size, split the node)


Association Rule Discovery: Hash tree

1 5 9

1 4 5 1 3 63 4 5 3 6 7

3 6 8

3 5 6

3 5 7

6 8 9

2 3 4

5 6 7

1 2 4

4 5 71 2 5

4 5 8

1,4,7

2,5,8

3,6,9

Hash Function Candidate Hash Tree

Hash on 1, 4 or 7



1 5 9

1 4 5 1 3 63 4 5 3 6 7

3 6 8

3 5 6

3 5 7

6 8 9

2 3 4

5 6 7

1 2 4

4 5 71 2 5

4 5 8

1,4,7

2,5,8

3,6,9


Hash on 2, 5 or 8



1 5 9

1 4 5 1 3 63 4 5 3 6 7

3 6 8

3 5 6

3 5 7

6 8 9

2 3 4

5 6 7

1 2 4

4 5 71 2 5

4 5 8

1,4,7

2,5,8

3,6,9


Hash on 3, 6 or 9


Subset Operation

1 2 3 5 6

Transaction, t

2 3 5 61 3 5 62

5 61 33 5 61 2 61 5 5 62 3 62 5

5 63

1 2 31 2 51 2 6

1 3 51 3 6

1 5 62 3 52 3 6

2 5 6 3 5 6

Subsets of 3 items

Level 1

Level 2

Level 3

63 5

Given a transaction t, what are the possible subsets of size 3?


Subset Operation Using Hash Tree

1 5 9

1 4 5 1 3 63 4 5 3 6 7

3 6 8

3 5 6

3 5 7

6 8 9

2 3 4

5 6 7

1 2 4

4 5 71 2 5

4 5 8

1 2 3 5 6

1 + 2 3 5 63 5 62 +

5 63 +

1,4,7

2,5,8

3,6,9

Hash Functiontransaction



1 5 9

1 4 5 1 3 63 4 5 3 6 7

3 6 8

3 5 6

3 5 7

6 8 9

2 3 4

5 6 7

1 2 4

4 5 71 2 5

4 5 8

1,4,7

2,5,8

3,6,9

Hash Function1 2 3 5 6

3 5 61 2 +

5 61 3 +

61 5 +

3 5 62 +

5 63 +

1 + 2 3 5 6

transaction



1 5 9

1 4 5 1 3 63 4 5 3 6 7

3 6 8

3 5 6

3 5 7

6 8 9

2 3 4

5 6 7

1 2 4

4 5 71 2 5

4 5 8

1,4,7

2,5,8

3,6,9

Hash Function1 2 3 5 6

3 5 61 2 +

5 61 3 +

61 5 +

3 5 62 +

5 63 +

1 + 2 3 5 6

transaction

Match transaction against 11 out of 15 candidates


Projected Database

TID Items1 {A,B}2 {B,C,D}3 {A,C,D,E}4 {A,D,E}5 {A,B,C}6 {A,B,C,D}7 {B,C}8 {A,B,C}9 {A,B,D}10 {B,C,E}

TID Items1 {B}2 {}3 {C,D,E}4 {D,E}5 {B,C}6 {B,C,D}7 {}8 {B,C}9 {B,D}10 {}

Original Database:Projected Database for node A:

For each transaction T, projected transaction at node A is T E(A)


ECLAT

For each item, store a list of transaction ids (tids)

TID Items1 A,B,E2 B,C,D3 C,E4 A,C,D5 A,B,C,D6 A,E7 A,B8 A,B,C9 A,C,D

10 B

HorizontalData Layout

A B C D E1 1 2 2 14 2 3 4 35 5 4 5 66 7 8 97 8 98 109

Vertical Data Layout

TID-list


ECLAT

Determine support of any k-itemset by intersecting tid-lists of two of its (k-1) subsets.

3 traversal approaches: – top-down, bottom-up and hybrid

Advantage: very fast support counting Disadvantage: intermediate tid-lists may become too large

for memory

A1456789

B1257810

AB1578


Rule Generation

Given a frequent itemset L, find all non-empty subsets f L such that f L – f satisfies the minimum confidence requirement– If {A,B,C,D} is a frequent itemset, candidate rules:

ABC D, ABD C, ACD B, BCD A, A BCD, B ACD, C ABD, D ABCAB CD, AC BD, AD BC, BC AD, BD AC, CD AB,

If |L| = k, then there are 2k – 2 candidate association rules (ignoring L and L)


Sequence Data

10 15 20 25 30 35

235

61

1

Timeline

Object A:

Object B:

Object C:

456

2 7812

16

178

Object Timestamp EventsA 10 2, 3, 5A 20 6, 1A 23 1B 11 4, 5, 6B 17 2B 21 7, 8, 1, 2B 28 1, 6C 14 1, 8, 7

Sequence Database:


Examples of Sequence Data

Sequence Database

Sequence Element (Transaction)

Event(Item)

Customer Purchase history of a given customer

A set of items bought by a customer at time t

Books, diary products, CDs, etc

Web Data Browsing activity of a particular Web visitor

A collection of files viewed by a Web visitor after a single mouse click

Home page, index page, contact info, etc

Event data History of events generated by a given sensor

Events triggered by a sensor at time t

Types of alarms generated by sensors

Genome sequences

DNA sequence of a particular species

An element of the DNA sequence

Bases A,T,G,C

Sequence

E1E2

E1E3

E2E3E4E2

Element (Transaction

)

Event (Item)


Formal Definition of a Sequence

A sequence is an ordered list of elements (transactions)

s = < e1 e2 e3 … >

– Each element contains a collection of events (items)

ei = {i1, i2, …, ik}

– Each element is attributed to a specific time or location

Length of a sequence, |s|, is given by the number of elements of the sequence

A k-sequence is a sequence that contains k events (items)


Examples of Sequence

Web sequence:

< {Homepage} {Electronics} {Digital Cameras} {Canon Digital Camera} {Shopping Cart} {Order Confirmation} {Return to Shopping} >

Sequence of initiating events causing the nuclear accident at 3-mile Island:(http://stellar-one.com/nuclear/staff_reports/summary_SOE_the_initiating_event.htm)

< {clogged resin} {outlet valve closure} {loss of feedwater} {condenser polisher outlet valve shut} {booster pumps trip} {main waterpump trips} {main turbine trips} {reactor pressure increases}>

Sequence of books checked out at a library:<{Fellowship of the Ring} {The Two Towers} {Return of the King}>


Formal Definition of a Subsequence

A sequence <a1 a2 … an> is contained in another sequence <b1 b2 … bm> (m ≥ n) if there exist integers i1 < i2 < … < in such that a1 bi1 , a2 bi1, …, an bin

The support of a subsequence w is defined as the fraction of data sequences that contain w

A sequential pattern is a frequent subsequence (i.e., a subsequence whose support is ≥ minsup)

Data sequence Subsequence Contain?

< {2,4} {3,5,6} {8} > < {2} {3,5} > Yes

< {1,2} {3,4} > < {1} {2} > No

< {2,4} {2,4} {2,5} > < {2} {4} > Yes


Sequential Pattern Mining: Definition

Given: – a database of sequences

– a user-specified minimum support threshold, minsup

Task:– Find all subsequences with support ≥ minsup


Sequential Pattern Mining: Challenge

Given a sequence: <{a b} {c d e} {f} {g h i}>– Examples of subsequences:

<{a} {c d} {f} {g} >, < {c d e} >, < {b} {g} >, etc.

How many k-subsequences can be extracted from a given n-sequence?

<{a b} {c d e} {f} {g h i}> n = 9

k=4: Y _ _ Y Y _ _ _ Y

<{a} {d e} {i}>

1264

9

:Answer

k

n


Sequential Pattern Mining: Example

Minsup = 50%

Examples of Frequent Subsequences:

< {1,2} > s=60%< {2,3} > s=60%< {2,4}> s=80%< {3} {5}> s=80%< {1} {2} > s=80%< {2} {2} > s=60%< {1} {2,3} > s=60%< {2} {2,3} > s=60%< {1,2} {2,3} > s=60%

Object Timestamp EventsA 1 1,2,4A 2 2,3A 3 5B 1 1,2B 2 2,3,4C 1 1, 2C 2 2,3,4C 3 2,4,5D 1 2D 2 3, 4D 3 4, 5E 1 1, 3E 2 2, 4, 5


Extracting Sequential Patterns

Given n events: i1, i2, i3, …, in

Candidate 1-subsequences: <{i1}>, <{i2}>, <{i3}>, …, <{in}>

Candidate 2-subsequences:<{i1, i2}>, <{i1, i3}>, …, <{i1} {i1}>, <{i1} {i2}>, …, <{in-1} {in}>

Candidate 3-subsequences:<{i1, i2 , i3}>, <{i1, i2 , i4}>, …, <{i1, i2} {i1}>, <{i1, i2} {i2}>, …,

<{i1} {i1 , i2}>, <{i1} {i1 , i3}>, …, <{i1} {i1} {i1}>, <{i1} {i1} {i2}>, …


Generalized Sequential Pattern (GSP)

Step 1: – Make the first pass over the sequence database D to yield all the 1-

element frequent sequences

Step 2:

Repeat until no new frequent sequences are found– Candidate Generation:

Merge pairs of frequent subsequences found in the (k-1)th pass to generate candidate sequences that contain k items

– Candidate Pruning: Prune candidate k-sequences that contain infrequent (k-1)-subsequences

– Support Counting: Make a new pass over the sequence database D to find the support for these

candidate sequences

– Candidate Elimination: Eliminate candidate k-sequences whose actual support is less than minsup


Candidate Generation

Base case (k=2): – Merging two frequent 1-sequences <{i1}> and <{i2}> will produce two

candidate 2-sequences: <{i1} {i2}> and <{i1 i2}>

General case (k>2):– A frequent (k-1)-sequence w1 is merged with another frequent

(k-1)-sequence w2 to produce a candidate k-sequence if the subsequence obtained by removing the first event in w1 is the same as the subsequence obtained by removing the last event in w2

The resulting candidate after merging is given by the sequence w1 extended with the last event of w2.

– If the last two events in w2 belong to the same element, then the last event in w2 becomes part of the last element in w1

– Otherwise, the last event in w2 becomes a separate element appended to the end of w1


Candidate Generation Examples

Merging the sequences w1=<{1} {2 3} {4}> and w2 =<{2 3} {4 5}> will produce the candidate sequence < {1} {2 3} {4 5}> because the last two events in w2 (4 and 5) belong to the same element

Merging the sequences w1=<{1} {2 3} {4}> and w2 =<{2 3} {4} {5}> will produce the candidate sequence < {1} {2 3} {4} {5}> because the last two events in w2 (4 and 5) do not belong to the same element

We do not have to merge the sequences w1 =<{1} {2 6} {4}> and w2 =<{1} {2} {4 5}> to produce the candidate < {1} {2 6} {4 5}> because if the latter is a viable candidate, then it can be obtained by merging w1 with < {1} {2 6} {5}>


GSP Example

< {1} {2} {3} >< {1} {2 5} >< {1} {5} {3} >< {2} {3} {4} >< {2 5} {3} >< {3} {4} {5} >< {5} {3 4} >

< {1} {2} {3} {4} >< {1} {2 5} {3} >< {1} {5} {3 4} >< {2} {3} {4} {5} >< {2 5} {3 4} >

< {1} {2 5} {3} >

Frequent3-sequences

CandidateGeneration

CandidatePruning


Timing Constraints (I)

{A B} {C} {D E}

<= ms

<= xg >ng

xg: max-gap

ng: min-gap

ms: maximum span


< {2,4} {3,5,6} {4,7} {4,5} {8} > < {6} {5} > Yes

< {1} {2} {3} {4} {5}> < {1} {4} > No

< {1} {2,3} {3,4} {4,5}> < {2} {3} {5} > Yes

< {1,2} {3} {2,3} {3,4} {2,4} {4,5}> < {1,2} {5} > No

xg = 2, ng = 0, ms= 4


Mining Sequential Patterns with Timing

Constraints

Approach 1:– Mine sequential patterns without timing constraints

– Postprocess the discovered patterns

Approach 2:– Modify GSP to directly prune candidates that violate

timing constraints

– Question: Does Apriori principle still hold?


Apriori Principle for Sequence Data

Object Timestamp EventsA 1 1,2,4A 2 2,3A 3 5B 1 1,2B 2 2,3,4C 1 1, 2C 2 2,3,4C 3 2,4,5D 1 2D 2 3, 4D 3 4, 5E 1 1, 3E 2 2, 4, 5

Suppose:

xg = 1 (max-gap)

ng = 0 (min-gap)

ms = 5 (maximum span)

minsup = 60%

<{2} {5}> support = 40%

but

<{2} {3} {5}> support = 60%

Problem exists because of max-gap constraint

No such problem if max-gap is infinite


Contiguous Subsequences

s is a contiguous subsequence of w = <e1>< e2>…< ek>

if any of the following conditions hold:1. s is obtained from w by deleting an item from either e1 or ek

2. s is obtained from w by deleting an item from any element ei that contains more than 2 items

3. s is a contiguous subsequence of s’ and s’ is a contiguous subsequence of w (recursive definition)

Examples: s = < {1} {2} > – is a contiguous subsequence of

< {1} {2 3}>, < {1 2} {2} {3}>, and < {3 4} {1 2} {2 3} {4} >

– is not a contiguous subsequence of < {1} {3} {2}> and < {2} {1} {3} {2}>


Modified Candidate Pruning Step

Without maxgap constraint:– A candidate k-sequence is pruned if at least one of its

(k-1)-subsequences is infrequent

With maxgap constraint:– A candidate k-sequence is pruned if at least one of its

contiguous (k-1)-subsequences is infrequent


Timing Constraints (II)

{A B} {C} {D E}

<= ms

<= xg >ng <= ws

xg: max-gap

ng: min-gap

ws: window size

ms: maximum span


< {2,4} {3,5,6} {4,7} {4,6} {8} > < {3} {5} > No

< {1} {2} {3} {4} {5}> < {1,2} {3} > Yes

< {1,2} {2,3} {3,4} {4,5}> < {1,2} {3,4} > Yes

xg = 2, ng = 0, ws = 1, ms= 5


Modified Support Counting Step

Given a candidate pattern: <{a, c}>– Any data sequences that contain

<… {a c} … >,<… {a} … {c}…> ( where time({c}) – time({a}) ≤ ws) <…{c} … {a} …> (where time({a}) – time({c}) ≤ ws)

will contribute to the support count of candidate pattern


Other Formulation

In some domains, we may have only one very long time series– Example:

monitoring network traffic events for attacks monitoring telecommunication alarm signals

Goal is to find frequent sequences of events in the time series– This problem is also known as frequent episode mining

E1

E2

E1

E2

E1

E2

E3

E4 E3 E4

E1

E2

E2 E4

E3 E5

E2

E3 E5

E1

E2 E3 E1

Pattern: <E1> <E3>


General Support Counting Schemes

p

Object's TimelineSequence: (p) (q)

Method Support Count

COBJ 1

1

CWIN 6

CMINWIN 4

p qp

q qp

qqp

2 3 4 5 6 7

CDIST_O 8

CDIST 5

Assume:

xg = 2 (max-gap)

ng = 0 (min-gap)

ws = 0 (window size)

ms = 2 (maximum span)


Frequent Subgraph Mining

Extend association rule mining to finding frequent subgraphs

Useful for Web Mining, computational chemistry, bioinformatics, spatial data sets, etc

Databases

Homepage

Research

ArtificialIntelligence

Data Mining


Graph Definitions

a

b a

c c

b

(a) Labeled Graph

pq

p

p

rs

tr

t

qp

a

a

c

b

(b) Subgraph

p

s

t

p

a

a

c

b

(c) Induced Subgraph

p

rs

tr

p


Challenges

Node may contain duplicate labels Support and confidence

– How to define them?

Additional constraints imposed by pattern structure– Support and confidence are not the only constraints

– Assumption: frequent subgraphs must be connected

Apriori-like approach: – Use frequent k-subgraphs to generate frequent (k+1)

subgraphsWhat is k?


Challenges…

Support: – number of graphs that contain a particular subgraph

Apriori principle still holds

Level-wise (Apriori-like) approach:– Vertex growing:

k is the number of vertices

– Edge growing: k is the number of edges


Vertex Growing

a

a

e

a

p

q

r

p

a

a

a

p

rr

d

G1 G2

p

000

00

00

0

1

q

rp

rp

qpp

MG

000

0

00

00

2

r

rrp

rp

pp

MG

a

a

a

p

q

r

ep

0000

0000

00

000

00

3

q

r

rrp

rp

qpp

MG

G3 = join(G1,G2)

dr+


Edge Growing

a

a

f

a

p

q

r

p

a

a

a

p

rr

f

G1 G2

p

a

a

a

p

q

r

fp

G3 = join(G1,G2)

r+


Apriori-like Algorithm

Find frequent 1-subgraphs Repeat

– Candidate generation Use frequent (k-1)-subgraphs to generate candidate k-subgraph

– Candidate pruning Prune candidate subgraphs that contain infrequent (k-1)-subgraphs

– Support counting Count the support of each remaining candidate

– Eliminate candidate k-subgraphs that are infrequent

In practice, it is not as easy. There are many other issues


Example: Dataset

a

b

e

c

p

q

rp

a

b

d

p

r

G1 G2

q

e

c

a

p q

r

b

p

G3

d

rd

r

(a,b,p) (a,b,q) (a,b,r) (b,c,p) (b,c,q) (b,c,r) … (d,e,r)G1 1 0 0 0 0 1 … 0G2 1 0 0 0 0 0 … 0G3 0 0 1 1 0 0 … 0G4 0 0 0 0 0 0 … 0

a eq

c

d

p p

p

G4

r


Example

p

a b c d ek=1FrequentSubgraphs

a b

pc d

pc e

qa e

rb d

pa b

d

r

pd c

e

p

(Pruned candidate)

Minimum support count = 2

k=2FrequentSubgraphs

k=3CandidateSubgraphs


Candidate Generation

In Apriori:– Merging two frequent k-itemsets will produce a

candidate (k+1)-itemset

In frequent subgraph mining (vertex/edge growing)– Merging two frequent k-subgraphs may produce more

than one candidate (k+1)-subgraph

Data Mining Association Analysis Introduction to Data Mining by Tan, Steinbach, Kumar ©...

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