Data Mining: Practical Machine Learning Tools and Techniques, Second Edition

4 . 5

M I N I N G   A S S O C I AT I O N   RU L E S

1 1 5

If humidity 

= normal and windy = false then play = yes

4/4

If humidity 

= normal and play = yes then windy = false

4/6

If windy 

= false and play = yes then humidity = normal

4/6

If humidity 

= normal then windy = false and play = yes

4/7

If windy 

= false then humidity = normal and play = yes

4/8

If play 

= yes then humidity = normal and windy = false

4/9

If – then humidity 

= normal and windy = false and play = yes

4/12

The figures at the right show the number of instances for which all three con-

ditions are true—that is, the coverage—divided by the number of instances for

which the conditions in the antecedent are true. Interpreted as a fraction, they

represent the proportion of instances on which the rule is correct—that is, its

accuracy. Assuming that the minimum specified accuracy is 100%, only the first

of these rules will make it into the final rule set. The denominators of the frac-

tions are readily obtained by looking up the antecedent expression in Table 4.10

(though some are not shown in the Table). The final rule above has no condi-

tions in the antecedent, and its denominator is the total number of instances in

the dataset.

Table 4.11 shows the final rule set for the weather data, with minimum cov-

erage 2 and minimum accuracy 100%, sorted by coverage. There are 58 rules, 3

with coverage 4, 5 with coverage 3, and 50 with coverage 2. Only 7 have two

conditions in the consequent, and none has more than two. The first rule comes

from the item set described previously. Sometimes several rules arise from the

same item set. For example, rules 9, 10, and 11 all arise from the four-item set

in row 6 of Table 4.10:

temperature 

= cool, humidity = normal, windy = false, play = yes

Table 4.10

(continued)

One-item sets

Two-item sets

Three-item sets

Four-item sets

. . .

. . .

. . .

38

humidity 

= normal

humidity 

= normal

windy 

= false (4)

windy 

= false

play 

= yes (4)

39

humidity 

= normal

humidity 

= high

play 

= yes (6)

windy 

= false

play 

= no (2)

40

humidity 

= high

windy 

= true (3)

. . .

. . .

47

windy 

= false

play 

= no (2)

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C H A P T E R   4

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A LG O R I T H M S : T H E   BA S I C   M E T H O D S

Table 4.11

Association rules for the weather data.

Association rule

Coverage

Accuracy

1

humidity 

= normal windy = false

fi

play 

= yes

4

100%

2

temperature 

= cool

fi

humidity 

= normal

4

100%

3

outlook 

= overcast

fi

play 

= yes

4

100%

4

temperature 

= cool play = yes

fi

humidity 

= normal

3

100%

5

outlook 

= rainy windy = false

fi

play 

= yes

3

100%

6

outlook 

= rainy play = yes

fi

windy 

= false

3

100%

7

outlook 

= sunny humidity = high

fi

play 

= no

3

100%

8

outlook 

= sunny play = no

fi

humidity 

= high

3

100%

9

temperature 

= cool windy = false

fi

humidity 

= normal

2

100%

play 

= yes

10

temperature 

= cool humidity = normal windy

fi

play 

= yes

2

100%

= false

11

temperature 

= cool windy = false play = yes

fi

humidity 

= normal

2

100%

12

outlook 

= rainy humidity = normal windy 

fi

play 

= yes

2

100%

= false

13

outlook 

= rainy humidity = normal play = yes

fi

windy 

= false

2

100%

14

outlook 

= rainy temperature = mild windy 

fi

play 

= yes

2

100%

= false

15

outlook 

= rainy temperature = mild play = yes

fi

windy 

= false

2

100%

16

temperature 

= mild windy = false play = yes

fi

outlook 

= rainy

2

100%

17

outlook 

= overcast temperature = hot

fi

windy 

= false

2

100%

play 

= yes

18

outlook 

= overcast windy = false

fi

temperature 

= hot

2

100%

play 

= yes

19

temperature 

= hot play = yes

fi

outlook 

= overcast

2

100%

windy 

= false

20

outlook 

= overcast temperature = hot windy

fi

play 

= yes

2

100%

= false

21

outlook 

= overcast temperature = hot play 

fi

windy 

= false

2

100%

= yes

22

outlook 

= overcast windy = false play = yes

fi

temperature 

= hot

2

100%

23

temperature 

= hot windy = false play = yes

fi

outlook 

= overcast

2

100%

24

windy 

= false play = no

fi

outlook 

= sunny

2

100%

humidity 

= high

25

outlook 

= sunny humidity = high windy = false

fi

play 

= no

2

100%

26

outlook 

= sunny windy = false play = no

fi

humidity 

= high

2

100%

27

humidity 

= high windy = false play = no

fi

outlook 

= sunny

2

100%

28

outlook 

= sunny temperature = hot

fi

humidity 

= high

2

100%

play 

= no

29

temperature 

= hot play = no

fi

outlook 

= sunny

2

100%

humidity 

= high

30

outlook 

= sunny temperature = hot humidity 

fi

play 

= no

2

100%

= high

31

outlook 

= sunny temperature = hot play = no

fi

humidity 

= high

2

100%

. . .

. . .

. . .

. . .

58

outlook 

= sunny temperature = hot

fi

humidity 

= high

2

100%

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