Lesson 3c - Strings
The last atomic data type R has to offer are strings. Strings represent characters and text in R.
Table of Contents
Lesson Objectives
- Learn about strings
- Explore some of the functions R has to offer for strings.
- Concatenate strings and variables together.
Creating a String
Strings in R need to be surrounded by double quotes “ “ or single quotes “ “
Don’t mix and match! You can’t have a string start with single quotes and end with double quotes.
Input
myString <- "Hello, World!"
myString
Output
[1] "Hello, World!"
Using Quotations Inside Strings
If you need to use single quotes ‘ ‘, use double quotes “ “ to define the string.
myString <- "I'm happy!"
If you need to use double quotes “ “, use single quotes ‘ ‘ to define the string.
myString <- 'He said "hello".'
If you need to use both single quotes ‘ ‘ and double quotes “ “, you need to put a backslash \ before every quotation you defined the string with.
myString <- "He said that \"He's happy\""
myString <- 'He said that "He\'s happy"'
String Concatenation
In R, there are two ways to concatenate (combine) strings. One is using the cat() function, the other uses the paste() function.
cat()
The cat() function can combine strings and variables together and display it in the console. This function is most often used to debug your code. It also gets rid of the quotation marks at the end, and turns any " and ' to their proper quote.
Input
myString <- "Johnny"
myString2 <- "said that \"He's happy\"."
cat(myString, myString2)
Output
Johnny said that "He's happy".
cat()does not create a newline at the end of the string, so sometimes it creates some funky output like the following:
To avoid this, add
\nat the end.
Don’t worry about the line with
for. All it does is loop the code, we’ll talk about it in lesson 5.
By default, variables are seperated by a space when using cat(). You can remove this space if you add sep="" within the brackets.
Input
myString <- "Tes"
myString2 <- "ting"
cat(myString, myString2, sep="")
Output
Testing
paste()
The other function that has the ability to concatenate variables together is paste(). It’s similar to cat(), but it returns the new string. This allows you to save the output to a new variable.
Input
myString <- "The first number is"
myInt <- 2
myString2 <- paste(myString, myInt)
myString2
Output
[1] "The first number is 2"
Just like with cat(), you can use the sep="" tag to remove spaces between the variables.
Other Useful String Functions
Finding the Length of a String
The nchar() function returns the number of characters in a string.
Input
myString <- "Hello!"
nchar(myString)
Output
[1] 6
Setting a String to UPPERCASE and lowercase
toupper() and tolower() converts a string to uppercase and lowercase.
Input
myString <- "Hello!"
toupper(myString)
tolower(myString)
Output
[1] "HELLO!"
[1] "hello!"
Getting a Substring
The substring() function takes in a variable, the index of the first character, and the index of the last character to create a substring.
In R, indexing starts at 1. In myString, “H” is at index 1.
Input
myString <- "Hello!"
substring(myString, 3, 5)
Output
[1] "llo"
Testing If a String Contains Another String
To test if a string contains another string, use grepl(needle, haystack, fixed=TRUE). Change the needle and haystack to be the string you’re searching for inside which string. If you are familiar with Regular Expression (RegEx) searching, you can get rid of fixed=TRUE to do a RegEx search.
grepl(needle, haystack, fixed=TRUE) is case-sensitive.
Input
grepl("intro", "introduction to r", fixed=TRUE)
grepl("intro", "Introduction to R", fixed=TRUE)
grepl("intro", "machine learning with r: linear regression", fixed=TRUE)
Output
[1] TRUE
[1] FALSE
[1] FALSE
Key Points / Summary
- Strings represent words and characters.
- The first character in a string is at index 1.
- You can concatenate variables together using
cat()andpaste()