R 匹配忽略大小写和特殊字符

Question

I have searched and found similar answers but not exactly what I need.

I want to identify matches in 2 strings, ignoring case and spaces and special characters.

list1 <- c('a', 'b', 'c')
list2 <- c('A', 'B', 'C')
list3 <- c('a-', 'B_', '- c')

All below should give the same output (1 2 3)

match(list1, list1)
match(list1, list2)
match(list1, list3)

I have tried str_detect(list1, regex(list2, ignore_case = TRUE)) but that doesn't give the same type of output (and I don't know how to incorporate the special characters/spaces in there.

Answer 1

You can create a regex that pulls out only the letters in the middle of the strings using gsub , and then convert them to lowercase. You can then use standard match on the result. Best to put all this in its own function:

list1 <- c('a', 'b', 'c')
list2 <- c('A', 'B', 'C')
list3 <- c('a-', 'B_', '- c')

match2 <- function(a, b)
{
  a <- tolower(gsub("(.*)([[:alpha:]]+)(.*)", "\\2", a))
  b <- tolower(gsub("(.*)([[:alpha:]]+)(.*)", "\\2", b))
  match(a, b)
}

match2(list1, list1)
#> [1] 1 2 3
match2(list1, list2)
#> [1] 1 2 3
match2(list1, list3)
#> [1] 1 2 3

^{Created on 2020-02-21 by the reprex package (v0.3.0)}

Answer 2

See that @Allan Cameron posted a very similar solution right before me... going to leave this anyways because different enough.. ?!

list1 <- c('a', 'b', 'c')
list2 <- c('A', 'B', 'C')
list3 <- c('a-', 'B_', '- c')

regex to replace any symbol that is not an alphabetic character with an empty string:

f <- function(x) {
  return(tolower(gsub("[^[:alpha:]]", "", x)))
}

match(f(list1), f(list2))
match(f(list1), f(list3))
match(f(list2), f(list3))