Extracting substrings

The str_sub() function in stringr extracts parts of strings based on their location. As with all stringr functions, the first argument, string, is a vector of strings. The arguments start and end specify the boundaries of the piece to extract in characters.

For example, str_sub(x, 1, 4) asks for the substring starting at the first character, up to the fourth character, or in other words the first four characters. Try it with my Batman's name:

str_sub(c("Bruce", "Wayne"), 1, 4)

Both start and end can be negative integers, in which case, they count from the end of the string. For example, str_sub(x, -4, -1), asks for the substring starting at the fourth character from the end, up to the first character from the end, i.e. the last four characters. Again, try it with Batman:

str_sub(c("Bruce", "Wayne"), -4, -1)

To practice, you'll use str_sub() to look at popular first and last letters for names.

This is a part of the course

“String Manipulation with stringr in R”

View Course

Exercise instructions

We've set up the same boy_names and girl_names vectors from the last exercise in your workspace.

Use str_sub() to extract the first letter of each name in boy_names. Save this to boy_first_letter.
Use table() on boy_first_letter to count up how many names start with each letter. Can you see which is most popular?
Repeat these steps, but now look at the last letter for boys' names.
Again repeat, but now look at the first letter for girls' names.
Finally, look at the last letter for girls' names.

Hands-on interactive exercise

Have a go at this exercise by completing this sample code.

# Extract first letter from boy_names
boy_first_letter <- ___

# Tabulate occurrences of boy_first_letter
___
  
# Extract the last letter in boy_names, then tabulate
boy_last_letter <- ___
___

# Extract the first letter in girl_names, then tabulate
girl_first_letter <- ___
___

# Extract the last letter in girl_names, then tabulate
girl_last_letter <- ___
___

Edit and Run Code