def generate_sample(self, start_state=None, size=1):
"""
Generator version of self.sample
Return Type:
------------
List of State namedtuples, representing the assignment to all variables of the model.
Examples:
---------
>>> from pgmpy.factors import Factor
>>> from pgmpy.inference import GibbsSampling
>>> from pgmpy.models import MarkovModel
>>> model = MarkovModel([('A', 'B'), ('C', 'B')])
>>> factor_ab = Factor(['A', 'B'], [2, 2], [1, 2, 3, 4])
>>> factor_cb = Factor(['C', 'B'], [2, 2], [5, 6, 7, 8])
>>> model.add_factors(factor_ab, factor_cb)
>>> gibbs = GibbsSampling(model)
>>> gen = gibbs.generate_sample(size=2)
>>> [sample for sample in gen]
[[State(var='C', state=1), State(var='B', state=1), State(var='A', state=0)],
[State(var='C', state=0), State(var='B', state=1), State(var='A', state=1)]]
"""
if start_state is None and self.state is None:
self.state = self.random_state()
else:
self.set_start_state(start_state)
for i in range(size):
for j, (var, st) in enumerate(self.state):
other_st = tuple(st for v, st in self.state if var != v)
next_st = sample_discrete(list(range(self.cardinalities[var])),
self.transition_models[var][other_st])[0]
self.state[j] = State(var, next_st)
yield self.state[:]
def forward_sample(self, size=1):
"""
Generates sample(s) from joint distribution of the bayesian network.
Parameters
----------
size: int
size of sample to be generated
Returns
-------
sampled: pandas.DataFrame
the generated samples
Examples
--------
>>> from pgmpy.models.BayesianModel import BayesianModel
>>> from pgmpy.factors.CPD import TabularCPD
>>> from pgmpy.inference.Sampling import BayesianModelSampling
>>> student = BayesianModel([('diff', 'grade'), ('intel', 'grade')])
>>> cpd_d = TabularCPD('diff', 2, [[0.6], [0.4]])
>>> cpd_i = TabularCPD('intel', 2, [[0.7], [0.3]])
>>> cpd_g = TabularCPD('grade', 3, [[0.3, 0.05, 0.9, 0.5], [0.4, 0.25,
... 0.08, 0.3], [0.3, 0.7, 0.02, 0.2]],
... ['intel', 'diff'], [2, 2])
>>> student.add_cpds(cpd_d, cpd_i, cpd_g)
>>> inference = BayesianModelSampling(student)
>>> inference.forward_sample(2)
diff intel grade
0 (diff, 1) (intel, 0) (grade, 1)
1 (diff, 1) (intel, 0) (grade, 2)
"""
sampled = DataFrame(index=range(size), columns=self.topological_order)
for node in self.topological_order:
cpd = self.cpds[node]
states = [st for var, st in cpd.variables[node]]
if cpd.evidence:
indices = [i for i, x in enumerate(self.topological_order) if x in cpd.evidence]
evidence = sampled.values[:, [indices]].tolist()
weights = list(map(lambda t: cpd.reduce(t[0], inplace=False).values, evidence))
sampled[node] = list(map(lambda t: State(node, t), sample_discrete(states, weights)))
else:
sampled[node] = list(map(lambda t: State(node, t),
sample_discrete(states, cpd.values, size)))
return sampled
def forward_sample(self, size=1, return_type="dataframe"):
"""
Generates sample(s) from joint distribution of the bayesian network.
Parameters
----------
size: int
size of sample to be generated
return_type: string (dataframe | recarray)
Return type for samples, either of 'dataframe' or 'recarray'.
Defaults to 'dataframe'
Returns
-------
sampled: A pandas.DataFrame or a numpy.recarray object depending upon return_type argument
the generated samples
Examples
--------
>>> from pgmpy.models.BayesianModel import BayesianModel
>>> from pgmpy.factors.discrete import TabularCPD
>>> from pgmpy.sampling import BayesianModelSampling
>>> student = BayesianModel([('diff', 'grade'), ('intel', 'grade')])
>>> cpd_d = TabularCPD('diff', 2, [[0.6], [0.4]])
>>> cpd_i = TabularCPD('intel', 2, [[0.7], [0.3]])
>>> cpd_g = TabularCPD('grade', 3, [[0.3, 0.05, 0.9, 0.5], [0.4, 0.25,
... 0.08, 0.3], [0.3, 0.7, 0.02, 0.2]],
... ['intel', 'diff'], [2, 2])
>>> student.add_cpds(cpd_d, cpd_i, cpd_g)
>>> inference = BayesianModelSampling(student)
>>> inference.forward_sample(size=2, return_type='recarray')
rec.array([(0, 0, 1), (1, 0, 2)], dtype=
[('diff', '<i8'), ('intel', '<i8'), ('grade', '<i8')])
"""
types = [(var_name, "int") for var_name in self.topological_order]
sampled = np.zeros(size, dtype=types).view(np.recarray)
pbar = tqdm(self.topological_order)
for node in pbar:
pbar.set_description(
"Generating for node: {node}".format(node=node))
cpd = self.model.get_cpds(node)
states = range(self.cardinality[node])
evidence = cpd.variables[:0:-1]
if evidence:
cached_values = self.pre_compute_reduce(variable=node)
evidence = np.vstack([sampled[i] for i in evidence])
weights = list(
map(lambda t: cached_values[tuple(t)], evidence.T))
else:
weights = cpd.values
sampled[node] = sample_discrete(states, weights, size)
return _return_samples(return_type, sampled)
def sample(self, start_state=None, size=1, return_type="dataframe"):
"""
Sample from the Markov Chain.
Parameters
----------
start_state: dict or array-like iterable
Representing the starting states of the variables. If None is passed, a random start_state is chosen.
size: int
Number of samples to be generated.
return_type: string (dataframe | recarray)
Return type for samples, either of 'dataframe' or 'recarray'.
Defaults to 'dataframe'
Returns
-------
sampled: A pandas.DataFrame or a numpy.recarray object depending upon return_type argument
the generated samples
Examples
--------
>>> from pgmpy.factors import DiscreteFactor
>>> from pgmpy.sampling import GibbsSampling
>>> from pgmpy.models import MarkovModel
>>> model = MarkovModel([('A', 'B'), ('C', 'B')])
>>> factor_ab = DiscreteFactor(['A', 'B'], [2, 2], [1, 2, 3, 4])
>>> factor_cb = DiscreteFactor(['C', 'B'], [2, 2], [5, 6, 7, 8])
>>> model.add_factors(factor_ab, factor_cb)
>>> gibbs = GibbsSampling(model)
>>> gibbs.sample(size=4, return_tupe='dataframe')
A B C
0 0 1 1
1 1 0 0
2 1 1 0
3 1 1 1
"""
if start_state is None and self.state is None:
self.state = self.random_state()
elif start_state is not None:
self.set_start_state(start_state)
types = [(var_name, "int") for var_name in self.variables]
sampled = np.zeros(size, dtype=types).view(np.recarray)
sampled[0] = tuple([st for var, st in self.state])
for i in tqdm(range(size - 1)):
for j, (var, st) in enumerate(self.state):
other_st = tuple(st for v, st in self.state if var != v)
next_st = sample_discrete(
list(range(self.cardinalities[var])),
self.transition_models[var][other_st],
)[0]
self.state[j] = State(var, next_st)
sampled[i + 1] = tuple([st for var, st in self.state])
return _return_samples(return_type, sampled)
def sample(self, start_state=None, size=1, return_type="dataframe"):
"""
Sample from the Markov Chain.
Parameters:
-----------
start_state: dict or array-like iterable
Representing the starting states of the variables. If None is passed, a random start_state is chosen.
size: int
Number of samples to be generated.
return_type: string (dataframe | recarray)
Return type for samples, either of 'dataframe' or 'recarray'.
Defaults to 'dataframe'
Returns
-------
sampled: A pandas.DataFrame or a numpy.recarray object depending upon return_type argument
the generated samples
Examples:
---------
>>> from pgmpy.factors import DiscreteFactor
>>> from pgmpy.inference import GibbsSampling
>>> from pgmpy.models import MarkovModel
>>> model = MarkovModel([('A', 'B'), ('C', 'B')])
>>> factor_ab = DiscreteFactor(['A', 'B'], [2, 2], [1, 2, 3, 4])
>>> factor_cb = DiscreteFactor(['C', 'B'], [2, 2], [5, 6, 7, 8])
>>> model.add_factors(factor_ab, factor_cb)
>>> gibbs = GibbsSampling(model)
>>> gibbs.sample(size=4, return_tupe='dataframe')
A B C
0 0 1 1
1 1 0 0
2 1 1 0
3 1 1 1
"""
if start_state is None and self.state is None:
self.state = self.random_state()
elif start_state is not None:
self.set_start_state(start_state)
types = [(var_name, 'int') for var_name in self.variables]
sampled = np.zeros(size, dtype=types).view(np.recarray)
sampled[0] = np.array([st for var, st in self.state])
for i in range(size - 1):
for j, (var, st) in enumerate(self.state):
other_st = tuple(st for v, st in self.state if var != v)
next_st = sample_discrete(list(range(self.cardinalities[var])),
self.transition_models[var][other_st])[0]
self.state[j] = State(var, next_st)
sampled[i + 1] = np.array([st for var, st in self.state])
return _return_samples(return_type, sampled)
def forward_sample(self, size=1, return_type='dataframe'):
"""
Generates sample(s) from joint distribution of the bayesian network.
Parameters
----------
size: int
size of sample to be generated
return_type: string (dataframe | recarray)
Return type for samples, either of 'dataframe' or 'recarray'.
Defaults to 'dataframe'
Returns
-------
sampled: A pandas.DataFrame or a numpy.recarray object depending upon return_type argument
the generated samples
Examples
--------
>>> from pgmpy.models.BayesianModel import BayesianModel
>>> from pgmpy.factors.discrete import TabularCPD
>>> from pgmpy.sampling import BayesianModelSampling
>>> student = BayesianModel([('diff', 'grade'), ('intel', 'grade')])
>>> cpd_d = TabularCPD('diff', 2, [[0.6], [0.4]])
>>> cpd_i = TabularCPD('intel', 2, [[0.7], [0.3]])
>>> cpd_g = TabularCPD('grade', 3, [[0.3, 0.05, 0.9, 0.5], [0.4, 0.25,
... 0.08, 0.3], [0.3, 0.7, 0.02, 0.2]],
... ['intel', 'diff'], [2, 2])
>>> student.add_cpds(cpd_d, cpd_i, cpd_g)
>>> inference = BayesianModelSampling(student)
>>> inference.forward_sample(size=2, return_type='recarray')
rec.array([(0, 0, 1), (1, 0, 2)],
dtype=[('diff', '<i8'), ('intel', '<i8'), ('grade', '<i8')])
"""
types = [(var_name, 'int') for var_name in self.topological_order]
sampled = np.zeros(size, dtype=types).view(np.recarray)
for node in self.topological_order:
cpd = self.model.get_cpds(node)
states = range(self.cardinality[node])
evidence = cpd.variables[:0:-1]
if evidence:
cached_values = self.pre_compute_reduce(variable=node)
evidence = np.vstack([sampled[i] for i in evidence])
weights = list(map(lambda t: cached_values[tuple(t)], evidence.T))
else:
weights = cpd.values
sampled[node] = sample_discrete(states, weights, size)
return _return_samples(return_type, sampled)
def sample(self, start_state=None, size=1):
"""
Sample from the Markov Chain.
Parameters:
-----------
start_state: dict or array-like iterable
Representing the starting states of the variables. If None is passed, a random start_state is chosen.
size: int
Number of samples to be generated.
Return Type:
------------
pandas.DataFrame
Examples:
---------
>>> from pgmpy.factors import Factor
>>> from pgmpy.inference import GibbsSampling
>>> from pgmpy.models import MarkovModel
>>> model = MarkovModel([('A', 'B'), ('C', 'B')])
>>> factor_ab = Factor(['A', 'B'], [2, 2], [1, 2, 3, 4])
>>> factor_cb = Factor(['C', 'B'], [2, 2], [5, 6, 7, 8])
>>> model.add_factors(factor_ab, factor_cb)
>>> gibbs = GibbsSampling(model)
>>> gibbs.sample(size=4)
A B C
0 0 1 1
1 1 0 0
2 1 1 0
3 1 1 1
"""
if start_state is None and self.state is None:
self.state = self.random_state()
elif start_state is not None:
self.set_start_state(start_state)
sampled = DataFrame(index=range(size), columns=self.variables)
sampled.loc[0] = [st for var, st in self.state]
for i in range(size - 1):
for j, (var, st) in enumerate(self.state):
other_st = tuple(st for v, st in self.state if var != v)
next_st = sample_discrete(
list(range(self.cardinalities[var])),
self.transition_models[var][other_st])[0]
self.state[j] = State(var, next_st)
sampled.loc[i + 1] = [st for var, st in self.state]
return sampled
def forward_sample(self, size=1):
"""
Generates sample(s) from joint distribution of the bayesian network.
Parameters
----------
size: int
size of sample to be generated
Returns
-------
sampled: pandas.DataFrame
the generated samples
Examples
--------
>>> from pgmpy.models.BayesianModel import BayesianModel
>>> from pgmpy.factors.CPD import TabularCPD
>>> from pgmpy.inference.Sampling import BayesianModelSampling
>>> student = BayesianModel([('diff', 'grade'), ('intel', 'grade')])
>>> cpd_d = TabularCPD('diff', 2, [[0.6], [0.4]])
>>> cpd_i = TabularCPD('intel', 2, [[0.7], [0.3]])
>>> cpd_g = TabularCPD('grade', 3, [[0.3, 0.05, 0.9, 0.5], [0.4, 0.25,
... 0.08, 0.3], [0.3, 0.7, 0.02, 0.2]],
... ['intel', 'diff'], [2, 2])
>>> student.add_cpds(cpd_d, cpd_i, cpd_g)
>>> inference = BayesianModelSampling(student)
>>> inference.forward_sample(2)
diff intel grade
0 1 0 1
1 1 0 2
"""
sampled = DataFrame(index=range(size), columns=self.topological_order)
for node in self.topological_order:
cpd = self.model.get_cpds(node)
states = range(self.cardinality[node])
evidence = cpd.variables[:0:-1]
if evidence:
cached_values = self.pre_compute_reduce(variable=node)
evidence = sampled.ix[:, evidence].values
weights = list(map(lambda t: cached_values[tuple(t)],
evidence))
else:
weights = cpd.values
sampled[node] = sample_discrete(states, weights, size)
return sampled
def generate_sample(self, start_state=None, size=1):
"""
Generator version of self.sample
Return Type:
------------
List of State namedtuples, representing the assignment to all variables of the model.
Examples:
---------
>>> from pgmpy.factors.discrete import DiscreteFactor
>>> from pgmpy.sampling import GibbsSampling
>>> from pgmpy.models import MarkovModel
>>> model = MarkovModel([('A', 'B'), ('C', 'B')])
>>> factor_ab = DiscreteFactor(['A', 'B'], [2, 2], [1, 2, 3, 4])
>>> factor_cb = DiscreteFactor(['C', 'B'], [2, 2], [5, 6, 7, 8])
>>> model.add_factors(factor_ab, factor_cb)
>>> gibbs = GibbsSampling(model)
>>> gen = gibbs.generate_sample(size=2)
>>> [sample for sample in gen]
[[State(var='C', state=1), State(var='B', state=1), State(var='A', state=0)],
[State(var='C', state=0), State(var='B', state=1), State(var='A', state=1)]]
"""
if start_state is None and self.state is None:
self.state = self.random_state()
elif start_state is not None:
self.set_start_state(start_state)
for i in range(size):
for j, (var, st) in enumerate(self.state):
other_st = tuple(st for v, st in self.state if var != v)
next_st = sample_discrete(list(range(self.cardinalities[var])),
self.transition_models[var][other_st])[0]
self.state[j] = State(var, next_st)
yield self.state[:]
def likelihood_weighted_sample(self,
evidence=None,
size=1,
return_type="dataframe"):
"""
Generates weighted sample(s) from joint distribution of the bayesian
network, that comply with the given evidence.
'Probabilistic Graphical Model Principles and Techniques', Koller and
Friedman, Algorithm 12.2 pp 493.
Parameters
----------
evidence: list of `pgmpy.factor.State` namedtuples
None if no evidence
size: int
size of sample to be generated
return_type: string (dataframe | recarray)
Return type for samples, either of 'dataframe' or 'recarray'.
Defaults to 'dataframe'
Returns
-------
sampled: A pandas.DataFrame or a numpy.recarray object depending upon return_type argument
the generated samples with corresponding weights
Examples
--------
>>> from pgmpy.factors.discrete import State
>>> from pgmpy.models.BayesianModel import BayesianModel
>>> from pgmpy.factors.discrete import TabularCPD
>>> from pgmpy.sampling import BayesianModelSampling
>>> student = BayesianModel([('diff', 'grade'), ('intel', 'grade')])
>>> cpd_d = TabularCPD('diff', 2, [[0.6], [0.4]])
>>> cpd_i = TabularCPD('intel', 2, [[0.7], [0.3]])
>>> cpd_g = TabularCPD('grade', 3, [[0.3, 0.05, 0.9, 0.5], [0.4, 0.25,
... 0.08, 0.3], [0.3, 0.7, 0.02, 0.2]],
... ['intel', 'diff'], [2, 2])
>>> student.add_cpds(cpd_d, cpd_i, cpd_g)
>>> inference = BayesianModelSampling(student)
>>> evidence = [State('diff', 0)]
>>> inference.likelihood_weighted_sample(evidence=evidence, size=2, return_type='recarray')
rec.array([(0, 0, 1, 0.6), (0, 0, 2, 0.6)],
dtype=[('diff', '<i8'), ('intel', '<i8'), ('grade', '<i8'), ('_weight', '<f8')])
"""
types = [(var_name, 'int') for var_name in self.topological_order]
types.append(('_weight', 'float'))
sampled = np.zeros(size, dtype=types).view(np.recarray)
sampled['_weight'] = np.ones(size)
evidence_dict = {var: st for var, st in evidence}
for node in self.topological_order:
cpd = self.model.get_cpds(node)
states = range(self.cardinality[node])
evidence = cpd.get_evidence()
if evidence:
evidence_values = np.vstack([sampled[i] for i in evidence])
cached_values = self.pre_compute_reduce(node)
weights = list(
map(lambda t: cached_values[tuple(t)], evidence_values.T))
if node in evidence_dict:
sampled[node] = evidence_dict[node]
for i in range(size):
sampled['_weight'][i] *= weights[i][
evidence_dict[node]]
else:
sampled[node] = sample_discrete(states, weights)
else:
if node in evidence_dict:
sampled[node] = evidence_dict[node]
for i in range(size):
sampled['_weight'][i] *= cpd.values[
evidence_dict[node]]
else:
sampled[node] = sample_discrete(states, cpd.values, size)
return _return_samples(return_type, sampled)
def likelihood_weighted_sample(self, evidence=None, size=1, return_type="dataframe"):
"""
Generates weighted sample(s) from joint distribution of the bayesian
network, that comply with the given evidence.
'Probabilistic Graphical Model Principles and Techniques', Koller and
Friedman, Algorithm 12.2 pp 493.
Parameters
----------
evidence: list of `pgmpy.factor.State` namedtuples
None if no evidence
size: int
size of sample to be generated
return_type: string (dataframe | recarray)
Return type for samples, either of 'dataframe' or 'recarray'.
Defaults to 'dataframe'
Returns
-------
sampled: A pandas.DataFrame or a numpy.recarray object depending upon return_type argument
the generated samples with corresponding weights
Examples
--------
>>> from pgmpy.factors.discrete import State
>>> from pgmpy.models.BayesianModel import BayesianModel
>>> from pgmpy.factors.discrete import TabularCPD
>>> from pgmpy.sampling import BayesianModelSampling
>>> student = BayesianModel([('diff', 'grade'), ('intel', 'grade')])
>>> cpd_d = TabularCPD('diff', 2, [[0.6], [0.4]])
>>> cpd_i = TabularCPD('intel', 2, [[0.7], [0.3]])
>>> cpd_g = TabularCPD('grade', 3, [[0.3, 0.05, 0.9, 0.5], [0.4, 0.25,
... 0.08, 0.3], [0.3, 0.7, 0.02, 0.2]],
... ['intel', 'diff'], [2, 2])
>>> student.add_cpds(cpd_d, cpd_i, cpd_g)
>>> inference = BayesianModelSampling(student)
>>> evidence = [State('diff', 0)]
>>> inference.likelihood_weighted_sample(evidence=evidence, size=2, return_type='recarray')
rec.array([(0, 0, 1, 0.6), (0, 0, 2, 0.6)],
dtype=[('diff', '<i8'), ('intel', '<i8'), ('grade', '<i8'), ('_weight', '<f8')])
"""
types = [(var_name, 'int') for var_name in self.topological_order]
types.append(('_weight', 'float'))
sampled = np.zeros(size, dtype=types).view(np.recarray)
sampled['_weight'] = np.ones(size)
evidence_dict = {var: st for var, st in evidence}
for node in self.topological_order:
cpd = self.model.get_cpds(node)
states = range(self.cardinality[node])
evidence = cpd.get_evidence()
if evidence:
evidence_values = np.vstack([sampled[i] for i in evidence])
cached_values = self.pre_compute_reduce(node)
weights = list(map(lambda t: cached_values[tuple(t)], evidence_values.T))
if node in evidence_dict:
sampled[node] = evidence_dict[node]
for i in range(size):
sampled['_weight'][i] *= weights[i][evidence_dict[node]]
else:
sampled[node] = sample_discrete(states, weights)
else:
if node in evidence_dict:
sampled[node] = evidence_dict[node]
for i in range(size):
sampled['_weight'][i] *= cpd.values[evidence_dict[node]]
else:
sampled[node] = sample_discrete(states, cpd.values, size)
return _return_samples(return_type, sampled)
def likelihood_weighted_sample(self, evidence=None, size=1):
"""
Generates weighted sample(s) from joint distribution of the bayesian
network, that comply with the given evidence.
'Probabilistic Graphical Model Principles and Techniques', Koller and
Friedman, Algorithm 12.2 pp 493.
Parameters
----------
evidence: list of `pgmpy.factor.State` namedtuples
None if no evidence
size: int
size of sample to be generated
Returns
-------
sampled: pandas.DataFrame
the generated samples with corresponding weights
Examples
--------
>>> from pgmpy.factors.Factor import State
>>> from pgmpy.models.BayesianModel import BayesianModel
>>> from pgmpy.factors.CPD import TabularCPD
>>> from pgmpy.inference.Sampling import BayesianModelSampling
>>> student = BayesianModel([('diff', 'grade'), ('intel', 'grade')])
>>> cpd_d = TabularCPD('diff', 2, [[0.6], [0.4]])
>>> cpd_i = TabularCPD('intel', 2, [[0.7], [0.3]])
>>> cpd_g = TabularCPD('grade', 3, [[0.3, 0.05, 0.9, 0.5], [0.4, 0.25,
... 0.08, 0.3], [0.3, 0.7, 0.02, 0.2]],
... ['intel', 'diff'], [2, 2])
>>> student.add_cpds(cpd_d, cpd_i, cpd_g)
>>> inference = BayesianModelSampling(student)
>>> evidence = {'diff': State(var='diff',state=0)}
>>> inference.likelihood_weighted_sample(evidence, 2)
intel diff grade _weight
0 (intel, 0) (diff, 0) (grade, 1) 0.6
1 (intel, 1) (diff, 0) (grade, 1) 0.6
"""
sampled = DataFrame(index=range(size), columns=self.topological_order)
sampled['_weight'] = np.ones(size)
evidence_dict = {var: st for var, st in evidence}
for node in self.topological_order:
cpd = self.cpds[node]
states = [st for var, st in cpd.variables[node]]
if cpd.evidence:
indices = [i for i, x in enumerate(self.topological_order) if x in cpd.evidence]
evidence = sampled.values[:, [indices]].tolist()
weights = list(map(lambda t: cpd.reduce(t[0], inplace=False).values, evidence))
if node in evidence_dict:
sampled[node] = (State(node, evidence_dict[node]), ) * size
for i in range(size):
sampled.loc[i, '_weight'] *= weights[i][evidence_dict[node]]
else:
sampled[node] = list(map(lambda t: State(node, t), sample_discrete(states, weights)))
else:
if node in evidence_dict:
sampled[node] = (State(node, evidence_dict[node]), ) * size
for i in range(size):
sampled.loc[i, '_weight'] *= cpd.values[evidence_dict[node]]
else:
sampled[node] = list(map(lambda t: State(node, t),
sample_discrete(states, cpd.values, size)))
return sampled
def likelihood_weighted_sample(self, evidence=None, size=1):
"""
Generates weighted sample(s) from joint distribution of the bayesian
network, that comply with the given evidence.
'Probabilistic Graphical Model Principles and Techniques', Koller and
Friedman, Algorithm 12.2 pp 493.
Parameters
----------
evidence: list of `pgmpy.factor.State` namedtuples
None if no evidence
size: int
size of sample to be generated
Returns
-------
sampled: pandas.DataFrame
the generated samples with corresponding weights
Examples
--------
>>> from pgmpy.factors.Factor import State
>>> from pgmpy.models.BayesianModel import BayesianModel
>>> from pgmpy.factors.CPD import TabularCPD
>>> from pgmpy.inference.Sampling import BayesianModelSampling
>>> student = BayesianModel([('diff', 'grade'), ('intel', 'grade')])
>>> cpd_d = TabularCPD('diff', 2, [[0.6], [0.4]])
>>> cpd_i = TabularCPD('intel', 2, [[0.7], [0.3]])
>>> cpd_g = TabularCPD('grade', 3, [[0.3, 0.05, 0.9, 0.5], [0.4, 0.25,
... 0.08, 0.3], [0.3, 0.7, 0.02, 0.2]],
... ['intel', 'diff'], [2, 2])
>>> student.add_cpds(cpd_d, cpd_i, cpd_g)
>>> inference = BayesianModelSampling(student)
>>> evidence = [State('diff', 0)]
>>> inference.likelihood_weighted_sample(evidence, 2)
intel diff grade _weight
0 0 0 1 0.6
1 1 0 1 0.6
"""
sampled = DataFrame(index=range(size), columns=self.topological_order)
sampled['_weight'] = np.ones(size)
evidence_dict = {var: st for var, st in evidence}
for node in self.topological_order:
cpd = self.model.get_cpds(node)
states = range(self.cardinality[node])
if cpd.evidence:
evidence = sampled.ix[:, cpd.evidence].values
cached_values = self.pre_compute_reduce(node)
weights = list(map(lambda t: cached_values[tuple(t)], evidence))
if node in evidence_dict:
sampled[node] = evidence_dict[node]
for i in range(size):
sampled.loc[i, '_weight'] *= weights[i][evidence_dict[node]]
else:
sampled[node] = sample_discrete(states, weights)
else:
if node in evidence_dict:
sampled[node] = evidence_dict[node]
for i in range(size):
sampled.loc[i, '_weight'] *= cpd.values[evidence_dict[node]]
else:
sampled[node] = sample_discrete(states, cpd.values, size)
return sampled
def sample(self,
evidence=None,
start_state=None,
size=1,
return_type="dataframe"):
"""
Sample from the Markov Chain.
Parameters:
-----------
start_state: dict or array-like iterable
Representing the starting states of the variables. If None is passed, a random start_state is chosen.
evidence: array-like iterable
Representing states of the evidence variables
size: int
Number of samples to be generated.
return_type: string (dataframe | recarray)
Return type for samples, either of 'dataframe' or 'recarray'.
Defaults to 'dataframe'
Returns
-------
sampled: A pandas.DataFrame or a numpy.recarray object depending upon return_type argument
the generated samples
Examples:
---------
>>> from pgmpy.models.BayesianModel import BayesianModel
>>> from pgmpy.factors.discrete import TabularCPD
>>> from GibbsSamplingWithEvidence import GibbsSampling
>>> student = BayesianModel([('diff', 'grade'), ('intel', 'grade')])
>>> cpd_d = TabularCPD('diff', 2, [[0.6], [0.4]])
>>> cpd_i = TabularCPD('intel', 2, [[0.7], [0.3]])
>>> cpd_g = TabularCPD('grade', 3, [[0.3, 0.05, 0.9, 0.5], [0.4, 0.25,
... 0.08, 0.3], [0.3, 0.7, 0.02, 0.2]],
... ['intel', 'diff'], [2, 2])
>>> student.add_cpds(cpd_d, cpd_i, cpd_g)
>>> gibbs_sampler = GibbsSampling(student)
>>> samples = gibbs_sampler.sample(size=5, evidence=[('grade',1)])
>>> print(samples)
diff grade intel
0 1 1 1
1 1 1 0
2 0 1 0
3 0 1 0
4 1 1 0
"""
if start_state is None and self.state is None:
self.state = self.random_state()
elif start_state is not None:
self.set_start_state(start_state)
#overwriting with evidence
if evidence is not None:
for j, (var, st) in enumerate(self.state):
for key, value in evidence.items():
#for k, (v_e, st_e) in enumerate(evidence):
if var == key:
#print(var, self.state[j])
self.state[j] = State(var, value)
types = [(var_name, 'int') for var_name in self.variables]
sampled = np.zeros(size, dtype=types).view(np.recarray)
sampled[0] = tuple([st for var, st in self.state])
for i in range(size - 1):
for j, (var, st) in enumerate(self.state):
# check for evidence
next_st = None
if evidence is not None:
for v_e, st_e in evidence.items():
if var == v_e:
next_st = st_e
if next_st is None:
other_st = tuple(st for v, st in self.state if var != v)
next_st = sample_discrete(
list(range(self.cardinalities[var])),
self.transition_models[var][other_st])[0]
self.state[j] = State(var, next_st)
sampled[i + 1] = tuple([st for var, st in self.state])
return _return_samples(return_type, sampled)