[R] regex -> negate a word
Rau at demogr.mpg.de
Sun Jan 18 19:35:43 CET 2009
let's assume I have a vector of character strings:
x <- c("abcdef", "defabc", "qwerty")
What I would like to find is the following: all elements where the word
'abc' does not appear (i.e. 3 in this case of 'x').
Since I am not really experienced with regular expressions, I started
slowly and thought I find all word were 'abc' actually does appear:
> grep(pattern="abc", x=x)
 1 2
So far, so good. Now I read that ^ is the negation operator. But it can
also denote the beginning of a string as in:
> grep(pattern="^abc", x=x)
Of course, we need to put it inside square brackets to negate the
> grep(pattern="[^abc]", x=x)
 1 2 3
But this is not what I want either.
I'd appreciate any help. I assume this is rather easy and
 http://www.zytrax.com/tech/web/regex.htm: The ^ (circumflex or
caret) inside square brackets negates the expression....
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