问题描述
我正在尝试实现Markov Random Field。其中，我想获得一个phi(A|B = 0,C = 1)的值。但是，使用证据选项时，会发生KeyError: 'B'。我不知道为什么会这样。
下面是代码。
from pgmpy.inference import VariableElimination
import numpy as np
pf_value = model.get_partition_function()
infer = VariableElimination(model)
AIB0C1_dist = infer.query(['A'],evidence={'B':0,'C':1}) # phi(A|B = 0,C = 1)
print('phi(A|B = 0,C = 1)')
print(AIB0C1_dist)
P_AIB0C1 = AIB0C1_dist.values/np.sum(AIB0C1_dist.values)
for val in P_AIB0C1:
print(val,'\n')
以下是错误的原因。
KeyError Traceback (most recent call last)
<ipython-input-22-1c3cb220fae0> in <module>
20 print(val,'\n')
21
---> 22 AIB0C1_dist = infer.query(['A'],C = 1)
23 print('phi(A|B = 0,C = 1)')
24 print(AIB0C1_dist)
~\anaconda3\lib\site-packages\pgmpy\inference\ExactInference.py in query(self,variables,evidence,elimination_order,joint,show_progress)
254 )
255
--> 256 return self._variable_elimination(
257 variables=variables,258 operation="marginalize",~\anaconda3\lib\site-packages\pgmpy\inference\ExactInference.py in _variable_elimination(self,operation,show_progress)
157 eliminated_variables = set()
158 # Get working factors and elimination order
--> 159 working_factors = self._get_working_factors(evidence)
160 elimination_order = self._get_elimination_order(
161 variables,show_progress=show_progress
~\anaconda3\lib\site-packages\pgmpy\inference\ExactInference.py in _get_working_factors(self,evidence)
43 for evidence_var in evidence:
44 for factor,origin in working_factors[evidence_var]:
---> 45 factor_reduced = factor.reduce(
46 [(evidence_var,evidence[evidence_var])],inplace=False
47 )
~\anaconda3\lib\site-packages\pgmpy\factors\discrete\discreteFactor.py in reduce(self,values,inplace)
453 phi.variables = [phi.variables[index] for index in var_index_to_keep]
454 phi.cardinality = phi.cardinality[var_index_to_keep]
--> 455 phi.del_state_names([var for var,_ in values])
456
457 phi.values = phi.values[tuple(slice_)]
~\anaconda3\lib\site-packages\pgmpy\utils\state_name.py in del_state_names(self,var_list)
92 """
93 for var in var_list:
---> 94 del self.state_names[var]
95 del self.name_to_no[var]
96 del self.no_to_name[var]
KeyError: 'B'
是否可以解决KeyError？
解决方法
改为使用self.state_names.get(var,"")。
我已经添加了state_names。 “ B”已定义为键。
from pgmpy.models import MarkovModel
from pgmpy.factors.discrete import DiscreteFactor
model = MarkovModel([('A','B'),('B','C'),('C','D'),('D','A')])
factor1 = DiscreteFactor(['A','B'],[2,2],[30,5,1,10],state_names={'A': [0,1],'B': [0,1]})
factor2 = DiscreteFactor(['B','C'],[100,100],'C': [0,1]})
factor3 = DiscreteFactor(['C','D'],[1,100,state_names={'C': [0,'D': [0,1]})
factor4 = DiscreteFactor(['D','A'],state_names={'D': [0,'A': [0,1]})
model.add_factors(factor1,factor2,factor3,factor4)
有证据的代码仍然有问题。