Problem
I think the package will be incomplete until we find a way to express groups of characters. Here's a challenge to express email pattern matching in rx:
Challenges
First of all, I dont know of the way to express single "word" character (alnum + _). We used rx_word to denote \\w+ and perhaps it should have been rx_word_char() %>% rx_one_or_more().
rx_char <- function(.data = NULL, value=NULL) {
if(missing(value))
return(paste0(.data, "\\w"))
paste0(.data, sanitize(value))
}I also extended rx_count to cases of ranges of input
rx_count <- function(.data = NULL, n = 1) {
if(length(n)>1){
n[is.na(n)]<-""
return(paste0(.data, "{", n[1], "," , n[length(n)], "}"))
}
paste0(.data, "{", n,"}")
}Finally, we dont have a way to express word boundaries (\\b) and it might be useful to denote them. We shall call this function rx_word_edge
rx_word_start <- function(.data = NULL){
paste0(.data, "\\b")
}
rx_word_end <- rx_word_startFinally, our biggest problem is that there's no way to express groups of characters, other than through rx_any_of(), but if we pass other rx expressions, values will be sanitized twice, meaning that we will get four backslashes before each symbol instead of two.
# this function is exactly like rx_any_of() but without sanitization
rx_group <- function(.data = NULL, value) {
paste0(.data, "[", value, "]")
}Solution
Here's what it looks like when we put all pieces together:
x <- rx_word_start() %>%
rx_group(
rx() %>%
rx_char() %>%
rx_char(".%+-")
) %>%
rx_one_or_more() %>%
rx_char("@") %>%
rx_group(
rx() %>%
rx_char() %>%
rx_char(".-")
) %>%
rx_one_or_more() %>%
rx_char(".") %>%
rx_alpha() %>%
rx_count(2:6) %>%
rx_word_end()
x
#> [1] "\\b[\\w\\.%\\+-]+@[\\w\\.-]+\\.[[:alpha:]]{2,6}\\b"
txt <- "This text contains email [email protected] and [email protected]. The latter is no longer valid."
regmatches(txt, gregexpr(x, txt, perl = TRUE))
#> [[1]]
#> [1] "[email protected]" "[email protected]"
stringr::str_extract_all(txt, x)
#> [[1]]
#> [1] "[email protected]" "[email protected]" The code works but I don't like it.
- Constructor
rx look redundant (I believe, there's a way to get rid of it entirely using specialized class, see below).
- It is not very clear what
rx_one_or_more() is referring to. I wonder if all functions should have rep argument with default option one and options some/any in addition to what rx_count does today.
- Should
rx_char() without arguments be called rx_wordchar?
- Should
rx_char() with arguments be called rx_literal() or rx_plain?
- We should be very explicit about sanitization of arguments. To the extent that we should just mention: "input will be sanitized".
rx_group is artificial construct, a duplicate of rx_any_of, but without sanitization. Here I see couple of solutions.
a. Allow "nested pipes" (as I have done above). Create S3 class and this way detect when type of value argument is not character, but rx_string. Input of this class do not need to be sanitized, because it has been sanitized at creation.
b. Do not allow "nested pipes". Instead define rx_any_of() to have ... and allow multiple arguments mixing functions and characters. Then hypotherical pipe would look like this:
rx_word_edge() %>%
rx_any_of(rx_wordchar(), ".%+-", rep="some") %>%
rx_literal("@") %>%
rx_any_of(rx_wordchar(), ".-", rep="some") %>%
rx_literal(".") %>%
rx_alpha(rep=2:6) %>%
rx_word_edge()It's a lot to digest, but somehow everything related to one particular problem. Happy to split the issue once we identify the issues worth tackling.
React
Typescript
Django
Laravel
Facebook
Microsoft
Google
Alibaba
D3
Tencent