Question 3. Copy the introductory example. The vector name stores the extracted names.

a. Use the tools of this chapter to rearrange the vector so that all elements conform to the standard first_name last_name.

library(stringr)
raw.data <-"555-1239Moe Szyslak(636) 555-0113Burns, C. Montgomery555-6542Rev. Timothy Lovejoy555 8904Ned Flanders636-555-3226Simpson, Homer5553642Dr. Julius Hibbert"
#extract raw data to get names
names <- unlist(str_extract_all(raw.data, "[[:alpha:]., ]{2,}"))
names
## [1] "Moe Szyslak"          "Burns, C. Montgomery" "Rev. Timothy Lovejoy"
## [4] "Ned Flanders"         "Simpson, Homer"       "Dr. Julius Hibbert"
#extract data to get phone number
phone <- unlist(str_extract_all(raw.data,"\\(?(\\d{3})?\\)?(-| )?\\d{3}(-| )?\\d{4}"))
phone
## [1] "555-1239"       "(636) 555-0113" "555-6542"       "555 8904"      
## [5] "636-555-3226"   "5553642"
#To remove Title and Middle initial 
temp_name<- unlist(str_replace_all(names, "[[:alpha:]]+\\. ", ""))

#To Remove Punctuation in name
Full_name<-str_replace_all(temp_name, "[[:punct:]]", "")

Full_name
## [1] "Moe Szyslak"      "Burns Montgomery" "Timothy Lovejoy" 
## [4] "Ned Flanders"     "Simpson Homer"    "Julius Hibbert"

I am tring to separate First_name and Last_name into different columns 

#Split Full name
temp <- strsplit(Full_name, " ")
#Create Matrix 
mat  <- matrix(unlist(temp), ncol=2, byrow=TRUE)
#convert Matrix into Data.Frame
df   <- as.data.frame(mat)
#combine with phone number
df   <- cbind(df, phone)
#give valid name to column name
colnames(df) <- c("First_name", "Last_name", "Phone")
df
##   First_name  Last_name          Phone
## 1        Moe    Szyslak       555-1239
## 2      Burns Montgomery (636) 555-0113
## 3    Timothy    Lovejoy       555-6542
## 4        Ned   Flanders       555 8904
## 5    Simpson      Homer   636-555-3226
## 6     Julius    Hibbert        5553642

b. Construct a logical vector indicating whether a character has a title (i.e., Rev. and Dr.) 

title <- str_detect(names, "Rev.|Dr.")
title
## [1] FALSE FALSE  TRUE FALSE FALSE  TRUE

c. Construct a logical vector indicating whether a character has a second name.

initial <- str_replace(names, "[[:alpha:]]{2,3}[.]", "")
initial <- str_count(initial, "\\w+")
initial <- initial > 2;
initial
## [1] FALSE  TRUE FALSE FALSE FALSE FALSE

Question 4. Describe the types of strings that conform to the following regular expressions and construct an example that is matched by the regular expression.

1. [0-9]+\$

Numeric characters only (0 to 9), any length >0, has to end with a “$” sign.

str_detect("888888$", "[0-9]+\\$")
## [1] TRUE

2. \b[a-z]{1,4}\b

Vectors containing strings with maximum 4 continuous characters lowercase letters from a to z at the beginning and at the end.

str_detect("abcdefgh", "\\b[a-z]{1,4}\\b")
## [1] FALSE

3. .*?\.txt$

this will return any string with any length that ends with ‘.txt’

str_detect("Sample1.txt", ".*?\\.txt$")
## [1] TRUE

4.\d{2}/\d{2}/\d{4}

Has to contain a string with: 2 digits, followed by string “/”, followed by 2 digits, followed by string “/”, and then followed by 4 digits. most likely date format e.g dd/mm/yyyy or mm/dd/yyyy.

str_detect("16/09/2018", "\\d{2}/\\d{2}/\\d{4}")
## [1] TRUE

5. <(.+?)>.+?</\1>

This will helps to backreferencing to return any string with in HTML Tags.

tag1 <- "<<h3>This is a heading</h3>
  <p>This is a paragraph.</p>"

str_extract_all(tag1, '<(.+?)>.+?</\\1>')
## [[1]]
## [1] "<h3>This is a heading</h3>"  "<p>This is a paragraph.</p>"
  1. Secret Message The following code hides a secret message. Crack it with R and regular expressions. Hint: Some of the characters are more revealing than others! The code snippet is also available in the materials at www.r-datacollection.com.

clcopCow1zmstc0d87wnkig7OvdicpNuggvhryn92Gjuwczi8hqrfpRxs5Aj5dwpn0Tanwo Uwisdij7Lj8kpf03AT5Idr3coc0bt7yczjatOaootj55t3Nj3ne6c4Sfek.r1w1YwwojigO d6vrfUrbz2.2bkAnbhzgv4R9i05zEcrop.wAgnb.SqoU65fPa1otfb7wEm24k6t3sR9zqe5 fy89n6Nd5t9kc4fE905gmc4Rgxo5nhDk!gr

secret_message<- paste("clcopCow1zmstc0d87wnkig7OvdicpNuggvhryn92Gjuwczi8hqrfpRxs5Aj5dwpn0TanwoUwisdij7Lj8kpf03AT5Idr3coc0bt7yczjatOaootj55t3Nj3ne6c4Sfek.r1w1YwwojigOd6vrfUrbz2.2bkAnbhzgv4R9i05zEcrop.wAgnb.SqoU65fPa1otfb7wEm24k6t3sR9zqe5fy89n6Nd5t9kc4fE905gmc4Rgxo5nhDk!gr")
#get all uppercase letters.
message <- unlist(str_extract_all(secret_message, "[[:upper:].]{1,}"))
#join all letters.
message <- str_replace_all(paste(message, collapse = ''), "[.]", " "); 
message
## [1] "CONGRATULATIONS YOU ARE A SUPERNERD"