Using backreferences in patterns
Backreferences can be useful in matching because they allow you to find repeated patterns or words. Using a backreference requires two things: you need to capture() the part of the pattern you want to reference, and then you refer to it with REF1.
Take a look at this pattern: capture(LOWER) %R% REF1. It matches and captures any lower case character, then is followed by the captured character: it detects repeated characters regardless of what character is repeated. To see it in action try this:
str_view(c("hello", "sweet", "kitten"),
pattern = capture(LOWER) %R% REF1)
If you capture more than one thing you can refer to them with REF2, REF3 etc. up to REF9, counting the captures from the left of the pattern.
Let's practice with boy_names again. You might notice a change in this dataset. We've converted all names to lower case; you'll learn how to do that in the next chapter.
This exercise is part of the course
String Manipulation with stringr in R
Hands-on interactive exercise
Have a go at this exercise by completing this sample code.
# Names with three repeated letters
repeated_three_times <- ___
# Test it
str_view(boy_names, pattern = repeated_three_times, match = TRUE)