R: Extract Substring Starting from End of String

You can use the following methods to extract a substring in R starting from the end of the string:

Method 1: Use Base R

#define function to extract n characters starting from end
substr_end <- function(x, n){
  substr(x, nchar(x)-n+1, nchar(x))
}

#extract 3 characters starting from end 
substr_end(my_string, 3)

Method 2: Use stringr Package

library(stringr)

#extract 3 characters starting from end  
str_sub(my_string, start = -3)

Both of these examples extract the last three characters from the string called my_string.

The following examples show how to use each method in practice with the following data frame:

#create data frame
df <- data.frame(team=c('Mavericks', 'Lakers', 'Hawks', 'Nets', 'Warriors'),
                 points=c(100, 143, 129, 113, 123))

#view data frame
df

       team points
1 Mavericks    100
2    Lakers    143
3     Hawks    129
4      Nets    113
5  Warriors    123

Example 1: Extract Substring Starting from End Using Base R

The following code shows how to define a custom function in base R and then use the function to extract the last three characters from each string in the team column:

#define function to extract n characters starting from end
substr_end <- function(x, n){
  substr(x, nchar(x)-n+1, nchar(x))
}

#create new column that extracts last 3 characters from team column
df$team_last3 <- substr_end(my_string, 3)

#view updated data frame
df

       team points team_last3
1 Mavericks    100        cks
2    Lakers    143        ers
3     Hawks    129        wks
4      Nets    113        ets
5  Warriors    123        ors

Notice that the new column called team_last3 contains the last three characters of each string in the team column of the data frame.

Example 2: Extract Substring Starting from End Using stringr Package

The following code shows how to use the str_sub() function from the stringr package in R to extract the last three characters from each string in the team column:

library(stringr)

#create new column that extracts last 3 characters from team column
df$team_last3 <- str_sub(df$team, start = -3)

#view updated data frame
df

       team points team_last3
1 Mavericks    100        cks
2    Lakers    143        ers
3     Hawks    129        wks
4      Nets    113        ets
5  Warriors    123        ors

Notice that the new column called team_last3 contains the last three characters of each string in the team column of the data frame.

This matches the results from the previous method using base R.