str_extract specific patterns (example)

Question

I\'m still a little confused by regex syntax. Can you please help me with these patterns:

_A00_A1234B_
_A00_A12345B_
_A1_A12345_

my approac

Answer 1

You can try

library(stringr)
str_extract(str2, "[A-Z][0-9]{4,5}[A-Z]?")
#[1] "A1234B"  "A12345B" "A12345" 

Here, the pattern looks for a capital letter [A-Z], followed by 4 or 5 digits [0-9]{4,5}, followed by a capital letter [A-Z] ?

Or you can use stringi which would be faster

library(stringi)
 stri_extract(str2, regex="[A-Z][0-9]{4,5}[A-Z]?")
 #[1] "A1234B"  "A12345B" "A12345" 

Or a base R option would be

 regmatches(str2,regexpr('[A-Z][0-9]{4,5}[A-Z]?', str2))
 #[1] "A1234B"  "A12345B" "A12345" 

data

str2 <- c('_A00_A1234B_', '_A00_A12345B_', '_A1_A12345_')