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aima-python/knowledge.py at master · TarrySingh/aima-python · GitHub
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"""Knowledge in learning, Chapter 19"""
from
random
import
shuffle
from
utils
import
powerset
from
collections
import
defaultdict
# ______________________________________________________________________________
def
current_best_learning
(
examples
,
h
,
examples_so_far
=
[]):
""" [Figure 19.2]
The hypothesis is a list of dictionaries, with each dictionary representing
a disjunction."""
if
not
examples
:
return
h
e
=
examples
[
0
]
if
is_consistent
(
e
,
h
):
return
current_best_learning
(
examples
[
1
:],
h
,
examples_so_far
+
[
e
])
elif
false_positive
(
e
,
h
):
for
h2
in
specializations
(
examples_so_far
+
[
e
],
h
):
h3
=
current_best_learning
(
examples
[
1
:],
h2
,
examples_so_far
+
[
e
])
if
h3
!=
'FAIL'
:
return
h3
elif
false_negative
(
e
,
h
):
for
h2
in
generalizations
(
examples_so_far
+
[
e
],
h
):
h3
=
current_best_learning
(
examples
[
1
:],
h2
,
examples_so_far
+
[
e
])
if
h3
!=
'FAIL'
:
return
h3
return
'FAIL'
def
specializations
(
examples_so_far
,
h
):
"""Specialize the hypothesis by adding AND operations to the disjunctions"""
hypotheses
=
[]
for
i
,
disj
in
enumerate
(
h
):
for
e
in
examples_so_far
:
for
k
,
v
in
e
.
items
():
if
k
in
disj
or
k
==
'GOAL'
:
continue
h2
=
h
[
i
].
copy
()
h2
[
k
]
=
'!'
+
v
h3
=
h
.
copy
()
h3
[
i
]
=
h2
if
check_all_consistency
(
examples_so_far
,
h3
):
hypotheses
.
append
(
h3
)
shuffle
(
hypotheses
)
return
hypotheses
def
generalizations
(
examples_so_far
,
h
):
"""Generalize the hypothesis. First delete operations
(including disjunctions) from the hypothesis. Then, add OR operations."""
hypotheses
=
[]
# Delete disjunctions
disj_powerset
=
powerset
(
range
(
len
(
h
)))
for
disjs
in
disj_powerset
:
h2
=
h
.
copy
()
for
d
in
reversed
(
list
(
disjs
)):
del
h2
[
d
]
if
check_all_consistency
(
examples_so_far
,
h2
):
hypotheses
+=
h2
# Delete AND operations in disjunctions
for
i
,
disj
in
enumerate
(
h
):
a_powerset
=
powerset
(
disj
.
keys
())
for
attrs
in
a_powerset
:
h2
=
h
[
i
].
copy
()
for
a
in
attrs
:
del
h2
[
a
]
if
check_all_consistency
(
examples_so_far
, [
h2
]):
h3
=
h
.
copy
()
h3
[
i
]
=
h2
.
copy
()
hypotheses
+=
h3
# Add OR operations
hypotheses
.
extend
(
add_or
(
examples_so_far
,
h
))
shuffle
(
hypotheses
)
return
hypotheses
def
add_or
(
examples_so_far
,
h
):
"""Adds an OR operation to the hypothesis. The AND operations in the disjunction
are generated by the last example (which is the problematic one)."""
ors
=
[]
e
=
examples_so_far
[
-
1
]
attrs
=
{
k
:
v
for
k
,
v
in
e
.
items
()
if
k
!=
'GOAL'
}
a_powerset
=
powerset
(
attrs
.
keys
())
for
c
in
a_powerset
:
h2
=
{}
for
k
in
c
:
h2
[
k
]
=
attrs
[
k
]
if
check_negative_consistency
(
examples_so_far
,
h2
):
h3
=
h
.
copy
()
h3
.
append
(
h2
)
ors
.
append
(
h3
)
return
ors
# ______________________________________________________________________________
def
check_all_consistency
(
examples
,
h
):
"""Check for the consistency of all examples under h"""
for
e
in
examples
:
if
not
is_consistent
(
e
,
h
):
return
False
return
True
def
check_negative_consistency
(
examples
,
h
):
"""Check if the negative examples are consistent under h"""
for
e
in
examples
:
if
e
[
'GOAL'
]:
continue
if
not
is_consistent
(
e
, [
h
]):
return
False
return
True
def
disjunction_value
(
e
,
d
):
"""The value of example e under disjunction d"""
for
k
,
v
in
d
.
items
():
if
v
[
0
]
==
'!'
:
# v is a NOT expression
# e[k], thus, should not be equal to v
if
e
[
k
]
==
v
[
1
:]:
return
False
elif
e
[
k
]
!=
v
:
return
False
return
True
def
guess_value
(
e
,
h
):
"""Guess value of example e under hypothesis h"""
for
d
in
h
:
if
disjunction_value
(
e
,
d
):
return
True
return
False
def
is_consistent
(
e
,
h
):
return
e
[
"GOAL"
]
==
guess_value
(
e
,
h
)
def
false_positive
(
e
,
h
):
if
e
[
"GOAL"
]
==
False
:
if
guess_value
(
e
,
h
):
return
True
return
False
def
false_negative
(
e
,
h
):
if
e
[
"GOAL"
]
==
True
:
if
not
guess_value
(
e
,
h
):
return
True
return
False
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