Machine Learning: Spam Detection Using The Naive Bayes Algorithm | R Programming

The Naive Bayes algorithm is a method to apply Thomas Bayes theorem to solve classification problems. It is considered naive because it gives equal importance to all the variables. It is one of the simplest and an effective algorithm used in machine learning for various classification ion problems.

Applications of Naive Bayes:

1. Email Filtering: It is used to classify emails as spam and helps filter emails.
2. Credit Approval: Banks and credit providers use it to identify potential clients who will not default on loans in future.
3. Medical Diagnosis: Based on the input in form of symptoms and other features it is widely used by hospitals to diagnose various medical conditions.

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Problem statement: identify or classify the SMS textual data into spam or ham.

Variables:
Type: 2 types, Spam or Ham.
Text: SMS data in form of text.

#Set working directory

>setwd("/Users/Planet Analytics/Documents/RDirectory")

# Read File

>Data <- read.csv("sms_spam.csv")

#Explore Variables

>names(Data)

#See the structure of the data 

>str(Data)

#Check the summary

>summary(Data)

#Check the top data points

>head(Data)

# Check the number of spams and hams

>table(Data$type)

#Create a corpus

>library(tm)

>library(SnowballC)

>corpus <- VCorpus(VectorSource(Data$text))

>inspect(head(corpus))

#Check the text in corpus

>lapply(head(corpus,1), as.character)

#Clean the text

>Clean_corpus <- tm_map(corpus, content_transformer(tolower))

>Clean_corpus <- tm_map(Clean_corpus, removeNumbers)

>Clean_corpus <- tm_map(Clean_corpus, removeWords,stopwords())

>Clean_corpus <- tm_map(Clean_corpus, removePunctuation)

>Clean_corpus <- tm_map(Clean_corpus, stemDocument)

>Clean_corpus <- tm_map(Clean_corpus, stripWhitespace)

>lapply(head(Clean_corpus,2), as.character)

#Tokenization of the corpus

>corpus_dtm <- DocumentTermMatrix(Clean_corpus)

#Creating Train and test dataset

>Train <- corpus_dtm[1:4574,]

>Test <- corpus_dtm[4575:5574,]

>TrainLabels <- Data[1:4574,]$type

>TestLabels <- Data[4575:5574,]$type

#check the proportion of ham and spam in Train and Test dataset

>prop.table(table(TrainLabels))

>prop.table(table(TestLabels))

#Creating indicator features 

>FreqWords <- findFreqTerms(Train, 10)

#Filter DTM to only include frequent terms

>TrainFreq <- Train[ ,FreqWords]

>TestFreq <- Test[ ,FreqWords]

#Conver counts into categorical form

>convert <- function(x){

  x <- ifelse(x > 0, "Yes", "No")

}

>TrainSet <- apply(TrainFreq, MARGIN = 2, convert)

>TestSet <- apply(TestFreq, MARGIN = 2, convert)

#Train the model

>library(e1071)

>Model <- naiveBayes(TrainSet, TrainLabels)

#predicting Spam or Ham on test set

>Predictions <- predict(Model, TestSet)

#Checking accuracy

>table(Predictions, TestLabels)

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