, -, , . .
. 18.10 , , 18.1 (.. , , 18.8). . "null", , . . , .
426 II. Prolog
, . , , : [ size - small, shape = compact, holes - 1]
nut ( holes = 1, shape = compact). , size = small .
null |
smell / screw |
("")
1~ 7
Large long compact other
\ / I \
Key nut null
pen
/
Key
. IS. 10. , , 18.1 ( . 18.8)
, , , . . ; , . .
, , , . . . , , .
. 18.11. , . - . , . , . 18.11, , , , , . , , , .
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18.
S,
;
S . , , , ,
- " " , , ,..^
- S .,..., S ;
- {) .., S...,S; , , , K3KV,,, v; :
'1 '2 ■■ S
. 18.11.
, .
-
1. S , , "null".
2. , .
3. S , S , , , . , S S. (class probability tree), . ( , , ).
4. . .
18.5.2. ""
"" . , (impurity) . ( ).
. . . . . ,
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II. Prolog
. , . . , 3, I, , :
V I = - iiplc) log2 p(c)
, {) - , S . . , , 1, 0. 1 = 0. , I , .
S . ':.... :
IresW = - p{v) L p(c I v) log, ( I v)
v , (v) v S, p(c I v) , , v. (v) ( | v) S.
. , . , , S , , , . Ires . . I ■.-... , ,
I (A) = -2^p[v) ioga <p(v> }
I () . :
Gain (A). I - Ires (A)
, .
, , , (binarization of attributes). . () , .
18.
, , , .. , . . ().
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, Gird, :
Gini = Zd p(i) p(j)
i ; . Gini :
Gini [A) = £j (!(v) ^ p(i | v) p(j | V)
v A, p(i | v] i, , v.
, , , . , . . , .
18.1. (. 18.1). , "size" "holes", . , , , p(nut) = 3/12[1 | holes=l) = 3/5.
18.2. D 25% . S 75% , , . , , , D ( D) -D ( ). S . S?