Combination Regmatches and Replacement for specific Character

Question

I've tried replace character which match with specific character or followed by "BT", but my codes failed. This is my codes:

df <- data.frame(
  exposure = c("123BT", "113BB", "116BB", "117BT")
)

df %>%
  mutate(
    exposure2 = case_when(exposure == regmatches("d+\\BT") ~ paste0("-", exposure),
                     TRUE ~ exposure)
  )

the error is:

Error: Problem with `mutate()` column `exposure2`.
i `exposure2 = case_when(...)`.
x argument "m" is missing, with no default
Run `rlang::last_error()` to see where the error occurred.

Whereas my target is:

df <- data.frame(
  exposure = c("123BT", "113BB", "116BB", "117BT"),
exposure2 = c(-123, 113, 116, -117)
)

Answer 1

I recommend you use library stringr, you can extract your numbers with regex (\\d)+:

library(stringr)
library(dplyr)

df %>%
  mutate(
    exposure2 = case_when(str_detect(exposure,"BT") ~ paste0("-", str_extract(exposure, "(\\d)+")),
                          TRUE ~ str_extract(exposure, "(\\d)+"))
  )

Output:

  exposure exposure2
1    123BT      -123
2    113BB       113
3    116BB       116
4    117BT      -117

If you still prefer use regmatches you can get same result with:

df %>%
  mutate(
    exposure2 = case_when(exposure %in% regmatches(exposure, regexpr("\\d+BT", exposure)) ~ paste0("-", regmatches(exposure, regexpr("\\d+", exposure))),
                          TRUE ~ regmatches(exposure, regexpr("\\d+", exposure)))
  )