Here is an example: ``` r string = "-3e9, 9E-2" pattern <- "([+-]?)(\\d+)(\\.\\d+)?[eE]([+-]?)(\\d+)" stringr::str_match_all(string = string, pattern = pattern) stringr::str_match(string = string, pattern = pattern) ``` `str_match` reports NA, while `str_match_all` reports an empty string.