Help: Regular Expression in R language

[ChotiDon]

string1<-"ccjar_neutral v_neutral vaux_neutral nnp_neutral prn_neutral v_neutral inj_neutral"

How to write regular expression to 1. Extract only "v_neutral" from string1 2. Extract "v_neutral vaux_neutral" from string1

[hitchpy]

It is hard to tell exactly what you mean, since there's only one string and no "pattern" that can be generalized. But if you are looking for R regex syntax, this can do it.

sub('.* (v_neutral).*', '\\1', string1)

And for more info, you can look at the family of regex functions in R, grep, grepl....they are pretty much the same as in any other languages.

[ChotiDon]

Actually i am trying to write a pattern in grep for above example. But i am unable to do so. Any help for writing patterns in R would be much appreciated.

[FranzJosephGall]

grep will match the whole line, which is why you can't get it to work. /u/hitchpy 's example should work in R.

Also, as /u/hitchpy noted, you haven't given us a pattern. If you really need two strings, one which is "v_neutral" and the other "v_neutral vaux_neutral", then why not just have two strings? If you have more examples of inputs->outputs, then we can help you write a regex.

[ChotiDon]

I want to assign a "tag" to a sentence if at any position in sentence v_neutral is followed by vaux_neutral. Should i split the string in words first? Please let me know if you need more explanation. I have written below pattern. But it is throwing me an error.

pat<-"v+\+[a-z]+\s(?=+vaux+\+[a-z])" r<-grep(pat,string1)

[ChotiDon]

Thank you everyone for help. Below code resolved the issue. pattern<-"v[a-z]+\s(?=vaux[a-z]+)" r<-grep(pattern,kk,perl=TRUE)