Using Base R

First up, let’s use base R functions to extract substrings from the end of a string. The substr function is your friend here.

Here’s a simple example:

# Define a string
my_string <- "Hello, world!"

# Extract the last 6 characters
substring_from_end <- substr(my_string, nchar(my_string) - 5, nchar(my_string))

# Print the result
print(substring_from_end)

[1] "world!"

Explanation:

• nchar(my_string) returns the total number of characters in my_string.
• nchar(my_string) - 5 calculates the starting position of the substring, counting from the end.
• substr(my_string, start, stop) extracts the substring from the start position to the stop position.

Using stringr

The stringr package makes string manipulation more straightforward and readable. We’ll use the str_sub function for this task.

First, install and load the stringr package if you haven’t already:

#install.packages("stringr")
library(stringr)

Now, let’s extract a substring from the end:

# Define a string
my_string <- "Hello, world!"

# Extract the last 6 characters using stringr
substring_from_end <- str_sub(my_string, -6, -1)

# Print the result
print(substring_from_end)

[1] "world!"

Explanation:

• str_sub(my_string, start, end) extracts the substring from the start to the end position.
• Negative indices in str_sub count from the end of the string. So -6 refers to the sixth character from the end, and -1 refers to the last character.

Using stringi

The stringi package is another powerful tool for string manipulation. We’ll use the stri_sub function here.

First, install and load the stringi package:

#install.packages("stringi")
library(stringi)

Let’s extract our substring:

# Define a string
my_string <- "Hello, world!"

# Extract the last 6 characters using stringi
substring_from_end <- stri_sub(my_string, from = -6, to = -1)

# Print the result
print(substring_from_end)

[1] "world!"

Explanation:

• stri_sub(my_string, from, to) works similarly to str_sub, using from and to parameters to define the start and end positions.
• Negative values count from the end of the string.