def __init__(self, sampleData, fileCorrecting): self.hmm = HMM() self.hmm.buildFromData(sampleData) self.marginal, self.emission, self.transition = self.hmm.persistHMM() self.actualStates, self.observations = self.parseFileCorrecting(fileCorrecting) self.beforeAndAfterStates = self.observations self.correctedText = None
class viterbi(object):
def __init__(self, sampleData, fileCorrecting):
self.hmm = HMM()
self.hmm.buildFromData(sampleData)
self.marginal, self.emission, self.transition = self.hmm.persistHMM()
self.actualStates, self.observations = self.parseFileCorrecting(fileCorrecting)
self.beforeAndAfterStates = self.observations
self.correctedText = None
def parseFileCorrecting(self, filename):
f = open(filename, "r")
actualStates = []
observations = []
for line in f:
if " " in line:
lineSplit = line.split(" ")
actualStates.append(lineSplit[0])
observations.append(lineSplit[1][0])
f.close()
return actualStates, observations
def determineProbableSequence(self):
self.beforeAndAfterStates = []
pathProbabilities = [{}]
path = {}
states = []
for i in range(ord("a"), ord("z") + 1):
states.append(chr(i))
states.append("_")
# Calculate Initial Probabilities
for state in states:
# V( (t = 0) , X(0) ) = P( E(0) | X(0) ) * P(state)
# Use logs since numbers can potentially be very small
pathProbabilities[0][state] = (
math.log(self.emission[(self.observations[0], state)])
+ math.log(self.marginal[state]))
path[state] = state
for obs in range(1, len(self.observations)): # Number of states we have
updatedPath = {}
pathProbabilities.append({})
# V( (t), X(t) ) = P( E(t) | X(t) ) * P( X(t) | X(t-1) ) * V( (t-1), X(t-1))
for curState in states:
stateProbs = {}
for prevState in states:
stateProbs[prevState] = (
math.log(self.emission[(self.observations[obs], curState)])
+ math.log(self.transition[(curState, prevState)])
+ pathProbabilities[obs-1][prevState]
)
nextState = max(stateProbs, key = stateProbs.get)
probOfNextState = stateProbs[nextState]
pathProbabilities[obs][curState] = probOfNextState
updatedPath[curState] = path[nextState] + curState
path = updatedPath
finalState = max(pathProbabilities[len(pathProbabilities)-1], key = pathProbabilities[len(pathProbabilities)-1].get)
correctedText = path[finalState]
correctedText = correctedText.replace("_", " ")
for char in path[finalState]:
self.beforeAndAfterStates.append(char)
self.correctedText = correctedText
def calculateErrorRate(self):
mismatches = 0.0
for i in range(0, len(self.beforeAndAfterStates) - 1):
if self.beforeAndAfterStates[i] != self.actualStates[i]:
mismatches += 1
return mismatches/len(self.beforeAndAfterStates)
def formatAndPrint(self, initialErrors, finalErrors):
for char in self.beforeAndAfterStates:
print char
print "\n\n"
print "Iintial Error Rate:", (initialErrors * 100), "%"
print "Final Error Rate:", (finalErrors * 100), "%"
