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Some Simple but Propably Useful Regex Examples with R-Package stringr...

I found that examples for the use of regex in R are rather rare. Thus, I will provide some examples from my own learning materials - mostly stolen from the help pages, with small but maybe illustrative adaptions. ps: I will extent this list of examples HERE occasionally..

library(stringr)

shopping_list <- c("bread & Apples §$%&/()=?4", "flouR", "sugar", "milk x2")
str_extract(shopping_list, "[A-Z].*[1-9]")
# this extracts partial strings starting with an upper-case letter
# and ending with a digit, for all elements of the input vector..
# "." period, any single case letter, "*" the preceding item will
# be matched zero or more times, ".*" regex for a string
# comprised of any item being repeated arbitrarily often.

# output:
[1] "Apples §$%&/()=?4" NA                  NA                  NA

str_extract(shopping_list, "[a-z]{1,4}")
# this extracts partial strings with lowercase repetitions of 4,
# for all elements of the input vector..

# output:
[1] "brea" "flou" "suga" "milk"

str_extract(shopping_list, "\\b[a-z]{1,4}\\b")
# this extracts whole words with lowercase repetitions of 4,
# for all elements of the input vector..

#output:
[1] NA     NA     NA     "milk"

str <- c("&George W. Bush", "Lyndon B. Johnson?")
gsub("[^[:alnum:][:space:].]", "", str)
# keep alphanumeric signs AND full-stop, remove anything else,
# that is, all other punctuation. what should not be matched is
# designated by the caret.

# output:
[1] "George W. Bush"    "Lyndon B. Johnson"