regex - How to Extract a substring that matches a Perticular Regular expression match from a String in R -

i trying write function can substrings string matches regular expression , example : -

str <- "hello brother how you" 

i want extract substrings str , substrings matches regular expression - "[a-z]+ [a-z]+"

which results in -

"hello brother" "brother how" "how are" "are you" 

is there library function can ?

you can stringr library str_match_all function , method tim pietzcker described in answer (capturing inside unanchored positive lookahead):

> library(stringr) > str <- "hello brother how you" > res <- str_match_all(str, "(?=\\b([[:alpha:]]+ [[:alpha:]]+))") > l <- unlist(res) > l[l != ""] ## [1] "hello brother" "brother how"   "how are"       "are you" 

or unqiue values:

> unique(l[l != ""]) ##[1] "hello brother" "brother how"   "how are"       "are you"       

i advise use [[:alpha:]] instead of [a-z] since pattern matches more letters.