R Regular Expression using "+" "?" or "*"

Question

From https://stringr.tidyverse.org/articles/regular-expressions.html

It describes controlling how many times a pattern shows up using:

• ?: 0 or 1.
• +: 1 or more.
• *: 0 or more.

So this works well:

str_view("hello123world", "123?")

However why not this?

str_view("cycyccyccccc", "ccc?")

The above highlights cc in the beginning of the string.

I was expecting it to highlight three c's in the last rows of c's at the end.

Answer 1

The regex you passed "ccc?" means (in words) "c followed by c followed by zero or one c's" so str_view gives you the first instance of two c's in a row (because that's c followed by c followed by zero c's).

If you'd like exactly 3 c's you could use

str_view("cycyccyccccc", "ccc")

Or if you'd like 3 or more c's you could use

str_view("cycyccyccccc", "c{3,}")