Using regex in R to find strings as whole words (but not strings as part of words)

I'm searching for the right regular expression. The following

t1 = c("IGF2, IGF2AS, INS, TH", "TH", "THZ开发者_JAVA百科H", "ZGTH")
grep("TH",t1, value=T)

returns all elements of t1, but only the first and second are correct. I just want entries with word/phrase TH returned?

You need to add word boundary anchors (\b) around your search strings so only entire words will be matched (i. e. words surrounded by non-word characters or start/end of string, where "word character" means \w, i.e. alphanumeric character).

Try

grep("\\bTH\\b",t3, value=T)

You can use \< and \> in a regexp to match at the beginning/end of the word.

grep ("\\<TH\\>", t1) etc.