grep - R: regular expression to specify end of string char is a letter -

grep - R: regular expression to specify end of string char is a letter -

string = c("hello-", "helloa", "helloa") grep("hello$[a-z]", string)

i wish find indices of strings in next character after word "hello" letter (case insensitive). code above doesn't work, grep() homecoming indices 2 , 3 since words have letter after "hello"

use positive lookahead

> string = c("hello-", "helloa", "helloa") > grep('hello(?=[a-za-z])', string, perl=t) [1] 2 3

(?=[a-za-z]) positive lookahead asserts character next string hello must letter.

or

> grep('hello[a-za-z]', string) [1] 2 3

add $ in regex if there 1 letter next string hello. $ asserts @ end.

> grep('hello[a-za-z]$', string) [1] 2 3 > grep('hello(?=[a-za-z]$)', string, perl=t) [1] 2 3

r grep