What is a "string"?

A string is a collection of characters placed between quotes.

A character is a single input from your keyboard (e.g. a single letter or a single punctuation mark).

string1 <- "Hi!"
string2 <- 'Hello, I am C-3PO, it is a pleasure to meet you.'

You can combine strings in a vector.

string3 <- c("It's against", "my programming", "to use inconsistent notation.")
string3

## [1] "It's against"                  "my programming"               
## [3] "to use inconsistent notation."

library(stringr)

... but it's also included in the tidyverse!

stringr provides many tools to work with strings, including functions that

• count the characters in a string: str_count()

• concatenate string vectors str_c()

• detect patterns str_detect()

• trim whitespace str_trim()

Begin with str_

All take a vector of strings as their first argument

Include a quotation in a string?

Why doesn't the code below work?

string3 <- "I say "Hello" to the class"

## Error: <text>:1:20: unexpected symbol
## 1: string3 <- "I say "Hello
##                        ^

To include a double quote in a string, escape it using a backslash \.

string4 <- "I say \"Hello\" to the class"

What if you want to include an actual backslash?

string5 <- "\\"

This may seem tedious but it will come up later!

writeLines

writeLines shows the contents of the string not including escapes.

string4

## [1] "I say \"Hello\" to the class"

writeLines(string4)

## I say "Hello" to the class

string5

## [1] "\\"

writeLines(string5)

## \

rockyou.txt

• RockYou developed software for social media platforms such as MySpace and Facebook

• Stored user passwords in plain text files

• Hacked in 2009 and over 32 million passwords leaked

Let's look at the first 20

rockyou20 <- rockyou[1:20] 
rockyou20

##  [1] "123456"    "12345"     "123456789" "password"  "iloveyou"  "princess" 
##  [7] "1234567"   "rockyou"   "12345678"  "abc123"    "nicole"    "daniel"   
## [13] "babygirl"  "monkey"    "lovely"    "jessica"   "654321"    "michael"  
## [19] "ashley"    "qwerty"

str_length

Given a string, return the number of characters.

password = "qwerty"
str_length(password)

## [1] 6

Given a vector of strings, return the number of characters in each string.

str_length(rockyou20)

##  [1] 6 5 9 8 8 8 7 7 8 6 6 6 8 6 6 7 6 7 6 6

rockyou20

##  [1] "123456"    "12345"     "123456789" "password"  "iloveyou"  "princess" 
##  [7] "1234567"   "rockyou"   "12345678"  "abc123"    "nicole"    "daniel"   
## [13] "babygirl"  "monkey"    "lovely"    "jessica"   "654321"    "michael"  
## [19] "ashley"    "qwerty"

str_c

Combine two or more strings.

str_c("My", "password", "is", "qwerty")

## [1] "Mypasswordisqwerty"

Use sep to specify how the strings are separated.

str_c("My", "password", "is", "qwerty", sep = " ")

## [1] "My password is qwerty"

str_to_lower and str_to_upper

Convert the case of a string from lower to upper or upper to lower.

str_to_upper(rockyou20)

##  [1] "123456"    "12345"     "123456789" "PASSWORD"  "ILOVEYOU"  "PRINCESS" 
##  [7] "1234567"   "ROCKYOU"   "12345678"  "ABC123"    "NICOLE"    "DANIEL"   
## [13] "BABYGIRL"  "MONKEY"    "LOVELY"    "JESSICA"   "654321"    "MICHAEL"  
## [19] "ASHLEY"    "QWERTY"

str_sub

Extract parts of a string from start to end, inclusive.

str_sub(rockyou20, 1, 4)

##  [1] "1234" "1234" "1234" "pass" "ilov" "prin" "1234" "rock" "1234" "abc1"
## [11] "nico" "dani" "baby" "monk" "love" "jess" "6543" "mich" "ashl" "qwer"

str_sub(rockyou20, -4, -1)

##  [1] "3456" "2345" "6789" "word" "eyou" "cess" "4567" "kyou" "5678" "c123"
## [11] "cole" "niel" "girl" "nkey" "vely" "sica" "4321" "hael" "hley" "erty"

str_sub and str_to_upper

Can combine str_sub and str_to_upper to capitalize each password.

str_sub(rockyou20, 1, 1) <- str_to_upper(str_sub(rockyou20, 1, 1))
rockyou20

##  [1] "123456"    "12345"     "123456789" "Password"  "Iloveyou"  "Princess" 
##  [7] "1234567"   "Rockyou"   "12345678"  "Abc123"    "Nicole"    "Daniel"   
## [13] "Babygirl"  "Monkey"    "Lovely"    "Jessica"   "654321"    "Michael"  
## [19] "Ashley"    "Qwerty"

str_sort

Sort a string. Here we sort in decreasing alphabetical order.

str_sort(rockyou20, decreasing = TRUE)

##  [1] "Rockyou"   "Qwerty"    "Princess"  "Password"  "Nicole"    "Monkey"   
##  [7] "Michael"   "Lovely"    "Jessica"   "Iloveyou"  "Daniel"    "Babygirl" 
## [13] "Ashley"    "Abc123"    "654321"    "123456789" "12345678"  "1234567"  
## [19] "123456"    "12345"

Regular Expressions

A regular expression is a sequence of characters that allows you to describe string patterns. We use them to search for patterns.

• extract a phone number from text data
• determine if an email address is valid
• determine if a password has the required number of letters, characters, and symbols
• count the number of times "statistics" occurs in a corpus of text
• ...

Basic Match

To demonstrate the power of regular expressions, let's see if any of the 32 million leaked passwords contain the exact phrase "dog"

str_subset(rockyou, "dog")[1:30]

##  [1] "catdog"      "hotdog"      "bulldogs"    "bulldog"     "doggie"     
##  [6] "bigdog"      "maddog"      "snoopdogg"   "puppydog"    "doggy"      
## [11] "dog123"      "snoopdog"    "ilovedogs"   "doggies"     "luckydog"   
## [16] "catdog1"     "dogdog"      "reddog"      "bulldog1"    "mollydog"   
## [21] "hotdog1"     "bulldogs1"   "dogcat"      "doggy1"      "hotdogs"    
## [26] "dogsrule"    "thedog"      "catsanddogs" "topdog"      "daisydog"

Basic Match

What about "d-g"? Match any character using .

str_subset(rockyou, "d.g")[1:30]

##  [1] "asdfgh"     "asdfghjkl"  "catdog"     "hotdog"     "bulldogs"  
##  [6] "bulldog"    "asdfg"      "doggie"     "bigdog"     "maddog"    
## [11] "digger"     "digimon"    "digital"    "candygirl"  "snoopdogg" 
## [16] "puppydog"   "doggy"      "dog123"     "snoopdog"   "asdfghj"   
## [21] "ilovedogs"  "doggies"    "asdfghjk"   "luckydog"   "catdog1"   
## [26] "indigo"     "dogdog"     "madagascar" "reddog"     "bulldog1"

Anchors

Match the start of a string using ^

str_view_all(rockyou20, "^P")

rockyou20

##  [1] "123456"    "12345"     "123456789" "password"  "iloveyou"  "princess" 
##  [7] "1234567"   "rockyou"   "12345678"  "abc123"    "nicole"    "daniel"   
## [13] "babygirl"  "monkey"    "lovely"    "jessica"   "654321"    "michael"  
## [19] "ashley"    "qwerty"

Anchors

Match the end of a string using $

str_view_all(rockyou20, "u$", match = TRUE)

str_detect

Determine if a character vector matches a pattern.

rockyou20

##  [1] "123456"    "12345"     "123456789" "password"  "iloveyou"  "princess" 
##  [7] "1234567"   "rockyou"   "12345678"  "abc123"    "nicole"    "daniel"   
## [13] "babygirl"  "monkey"    "lovely"    "jessica"   "654321"    "michael"  
## [19] "ashley"    "qwerty"

str_detect(rockyou20, "a")

##  [1] FALSE FALSE FALSE  TRUE FALSE FALSE FALSE FALSE FALSE  TRUE FALSE  TRUE
## [13]  TRUE FALSE FALSE  TRUE FALSE  TRUE  TRUE FALSE

str_count

How many matches are there in a string?

rockyou20

##  [1] "123456"    "12345"     "123456789" "password"  "iloveyou"  "princess" 
##  [7] "1234567"   "rockyou"   "12345678"  "abc123"    "nicole"    "daniel"   
## [13] "babygirl"  "monkey"    "lovely"    "jessica"   "654321"    "michael"  
## [19] "ashley"    "qwerty"

str_count(rockyou20, "s")

##  [1] 0 0 0 2 0 2 0 0 0 0 0 0 0 0 0 2 0 0 1 0

str_replace_all

Replace all matches with new strings.

str_replace_all(rockyou20, "s", "-")

##  [1] "123456"    "12345"     "123456789" "pa--word"  "iloveyou"  "prince--" 
##  [7] "1234567"   "rockyou"   "12345678"  "abc123"    "nicole"    "daniel"   
## [13] "babygirl"  "monkey"    "lovely"    "je--ica"   "654321"    "michael"  
## [19] "a-hley"    "qwerty"

Many Matches

The regular expressions below match more than one character.

• Match any digit using \d or [[:digit:]]
• Match any whitespace using \s or [[:space:]]
• Match f, g, or h using [fgh]
• Match anything but f, g, or h using [^fgh]
• Match lower-case letters using [a-z] or [[:lower:]]
• Match upper-case letters using [A-Z] or [[:upper:]]
• Match alphabetic characters using [A-z] or [[:alpha:]]

Remember these are regular expressions! To match digits you'll need to escape the string, so use "\\d", not "\d"

Additional resources

• stringr website: https://stringr.tidyverse.org/
• stringr and regex cheat sheet
• Chapter 14: Strings in R for Data Science