Replace all strings which do not include at least one letter

Question

I want to delete strings which contains only special characters. If there is at least one letter or number the string should be left as is.

test_cases <- c("a", "&", "&& ", "& &", "& ", "&a", "& a", "1", "& 1", "&1", "& a d", "a ")
exp_out <- c("a", "", "", "", "", "&a", "& a", "1", "& 1", "&1", "& a d", "a ")

I used a negative look ahead for that:

gsub("^[^a-zA-Z0-9]+(?! *[a-zA-Z0-9]+ *)", "", test_cases, perl = TRUE)
# [1] "a"     ""      ""      ""      ""      "&a"    "& a"   "1"     "& 1"   "&1"    "& a d" "a "

This regex seems to be rather verbose and while testing I had to adapt it several times, because I forgot some edge cases. Thus, I was wondering whether I can come up with a "simpler" regex, that is a regex which is shorter?

Answer 1

You may use

test_cases[!grepl("[[:alpha:][:digit:]]", test_cases)] <- ""

See the R demo

The !grepl("[[:alpha:][:digit:]]", test_cases) command will only fetch the items that do not contain any letter ([:alpha:]) or digit ([:digit:]).

Output

 [1] "a"     ""      ""      ""      ""      "&a"    "& a"   "1"     "& 1"  
[10] "&1"    "& a d" "a "