diff --git a/README.md b/README.md
index 2ed47475d..d7ba58b33 100644
--- a/README.md
+++ b/README.md
@@ -109,7 +109,7 @@ Here is a table of algorithms, the figure, name of the code in the book and in t
| 18.24 | Back-Prop-Learning | `BackPropagationLearner` | [`learning.py`][learning] |
| 18.34 | AdaBoost | `AdaBoost` | [`learning.py`][learning] |
| 19.2 | Current-Best-Learning | `current_best_learning` | [`knowledge.py`](knowledge.py) |
-| 19.3 | Version-Space-Learning | |
+| 19.3 | Version-Space-Learning | `version_space_learning` | [`knowledge.py`](knowledge.py) |
| 19.8 | Minimal-Consistent-Det | |
| 19.12 | FOIL | |
| 21.2 | Passive-ADP-Agent | `PassiveADPAgent` | [`rl.py`][rl] |
diff --git a/knowledge.py b/knowledge.py
index 106176c19..a42640bfd 100644
--- a/knowledge.py
+++ b/knowledge.py
@@ -81,7 +81,10 @@ def generalizations(examples_so_far, h):
hypotheses += h3
# Add OR operations
- hypotheses.extend(add_or(examples_so_far, h))
+ if hypotheses == [] or hypotheses == [{}]:
+ hypotheses = add_or(examples_so_far, h)
+ else:
+ hypotheses.extend(add_or(examples_so_far, h))
shuffle(hypotheses)
return hypotheses
@@ -111,6 +114,97 @@ def add_or(examples_so_far, h):
# ______________________________________________________________________________
+def version_space_learning(examples):
+ """ [Figure 19.3]
+ The version space is a list of hypotheses, which in turn are a list
+ of dictionaries/disjunctions."""
+ V = all_hypotheses(examples)
+ for e in examples:
+ if V:
+ V = version_space_update(V, e)
+
+ return V
+
+
+def version_space_update(V, e):
+ return [h for h in V if is_consistent(e, h)]
+
+
+def all_hypotheses(examples):
+ """Builds a list of all the possible hypotheses"""
+ values = values_table(examples)
+ h_powerset = powerset(values.keys())
+ hypotheses = []
+ for s in h_powerset:
+ hypotheses.extend(build_attr_combinations(s, values))
+
+ hypotheses.extend(build_h_combinations(hypotheses))
+
+ return hypotheses
+
+
+def values_table(examples):
+ """Builds a table with all the possible values for each attribute.
+ Returns a dictionary with keys the attribute names and values a list
+ with the possible values for the corresponding attribute."""
+ values = defaultdict(lambda: [])
+ for e in examples:
+ for k, v in e.items():
+ if k == 'GOAL':
+ continue
+
+ mod = '!'
+ if e['GOAL']:
+ mod = ''
+
+ if mod + v not in values[k]:
+ values[k].append(mod + v)
+
+ values = dict(values)
+ return values
+
+
+def build_attr_combinations(s, values):
+ """Given a set of attributes, builds all the combinations of values.
+ If the set holds more than one attribute, recursively builds the
+ combinations."""
+ if len(s) == 1:
+ # s holds just one attribute, return its list of values
+ k = values[s[0]]
+ h = [[{s[0]: v}] for v in values[s[0]]]
+ return h
+
+ h = []
+ for i, a in enumerate(s):
+ rest = build_attr_combinations(s[i+1:], values)
+ for v in values[a]:
+ o = {a: v}
+ for r in rest:
+ t = o.copy()
+ for d in r:
+ t.update(d)
+ h.append([t])
+
+ return h
+
+
+def build_h_combinations(hypotheses):
+ """Given a set of hypotheses, builds and returns all the combinations of the
+ hypotheses."""
+ h = []
+ h_powerset = powerset(range(len(hypotheses)))
+
+ for s in h_powerset:
+ t = []
+ for i in s:
+ t.extend(hypotheses[i])
+ h.append(t)
+
+ return h
+
+# ______________________________________________________________________________
+
+
def check_all_consistency(examples, h):
"""Check for the consistency of all examples under h"""
for e in examples:
diff --git a/tests/test_knowledge.py b/tests/test_knowledge.py
index d9822c625..025da5ddd 100644
--- a/tests/test_knowledge.py
+++ b/tests/test_knowledge.py
@@ -23,6 +23,37 @@ def test_current_best_learning():
assert values == [True, True, True, False, False, False, True]
+ examples = trivial
+ initial_h = [{'Pizza': 'Yes'}]
+ h = current_best_learning(examples, initial_h)
+ values = []
+ for e in examples:
+ values.append(guess_value(e, h))
+
+ assert values == [True, True, False]
+
+
+def test_version_space_learning():
+ V = version_space_learning(trivial)
+ results = []
+ for e in trivial:
+ guess = False
+ for h in V:
+ if guess_value(e, h):
+ guess = True
+ break
+
+ results.append(guess)
+
+ assert results == [True, True, False]
+ assert [{'Pizza': 'Yes'}] in V
+
+
+trivial = [
+ {'Pizza': 'Yes', 'Soda': 'No', 'GOAL': True},
+ {'Pizza': 'Yes', 'Soda': 'Yes', 'GOAL': True},
+ {'Pizza': 'No', 'Soda': 'No', 'GOAL': False}
+]
animals_umbrellas = [
{'Species': 'Cat', 'Rain': 'Yes', 'Coat': 'No', 'GOAL': True},
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