5.Naive Bayesian Classifier

import csv
import random
import math
def loadCsv(filename):
lines = csv.reader(open(filename, "r"));
dataset = list(lines)
for i in range(len(dataset)):
#converting strings into numbers for processing
dataset[i] = [float(x) for x in dataset[i]]
return dataset
def splitDataset(dataset, splitRatio):
#67% training size
trainSize = int(len(dataset) * splitRatio);
trainSet = []
copy = list(dataset);
while len(trainSet) < trainSize:
#generate indices for the dataset list randomly to pick ele for training data
index = random.randrange(len(copy));
trainSet.append(copy.pop(index))
return [trainSet, copy]
def separateByClass(dataset):
separated = {}
#creates a dictionary of classes 1 and 0 where the values are the instacnes belonging to
each class
for i in range(len(dataset)):
vector = dataset[i]
if (vector[-1] not in separated):
separated[vector[-1]] = []
separated[vector[-1]].append(vector)
return separated
def mean(numbers):
return sum(numbers)/float(len(numbers))
def stdev(numbers):
avg = mean(numbers)
variance = sum([pow(x-avg,2) for x in numbers])/float(len(numbers)-1)
return math.sqrt(variance)
def summarize(dataset):
summaries = [(mean(attribute), stdev(attribute)) for attribute in zip(*dataset)];
del summaries[-1]
return summaries
def summarizeByClass(dataset):
separated = separateByClass(dataset);
summaries = {}
for classValue, instances in separated.items():
#summaries is a dic of tuples(mean,std) for each class value
summaries[classValue] = summarize(instances)
return summaries
def calculateProbability(x, mean, stdev):
exponent = math.exp(-(math.pow(x-mean,2)/(2*math.pow(stdev,2))))
return (1 / (math.sqrt(2*math.pi) * stdev)) * exponent
def calculateClassProbabilities(summaries, inputVector):
probabilities = {}
for classValue, classSummaries in summaries.items():#class and attribute information
as mean and sd
probabilities[classValue] = 1
for i in range(len(classSummaries)):
mean, stdev = classSummaries[i] #take mean and sd of every attribute
for class 0 and 1 seperaely
x = inputVector[i] #testvector's first attribute
probabilities[classValue] *= calculateProbability(x, mean, stdev);#use
normal dist
return probabilities
def predict(summaries, inputVector):
probabilities = calculateClassProbabilities(summaries, inputVector)
bestLabel, bestProb = None, -1
for classValue, probability in probabilities.items():#assigns that class which has he
highest prob
if bestLabel is None or probability > bestProb:
bestProb = probability
bestLabel = classValue
return bestLabel
def getPredictions(summaries, testSet):
predictions = []
for i in range(len(testSet)):
result = predict(summaries, testSet[i])
predictions.append(result)
return predictions
def getAccuracy(testSet, predictions):
correct = 0
for i in range(len(testSet)):
if testSet[i][-1] == predictions[i]:
correct += 1
return (correct/float(len(testSet))) * 100.0
def main():
filename = '5data.csv'
splitRatio = 0.67
dataset = loadCsv(filename);
trainingSet, testSet = splitDataset(dataset, splitRatio)
print('Split {0} rows into train={1} and test={2} rows'.format(len(dataset),
len(trainingSet), len(testSet)))
# prepare model
summaries = summarizeByClass(trainingSet);
# test model
predictions = getPredictions(summaries, testSet)
accuracy = getAccuracy(testSet, predictions)
print('Accuracy of the classifier is : {0}%'.format(accuracy))
main()