[R] regex -> negate a word

[Eric Archer]

Roland,

I think you were almost there with your first example.  Howabout using:

 > x <- c("abcdef", "defabc", "qwerty")
 > y <- grep(pattern="abc", x=x)
 > z.char <- x[-y]
 > z.index <- (1:length(x))[-y]
 >
 > z.char
[1] "qwerty"
 > z.index
[1] 3

Cheers,
eric

Rau, Roland wrote:
> Dear all,
> 
> 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] 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)
> [1] 1
> 
> Of course, we need to put it inside square brackets to negate the
> expression [1]
>> grep(pattern="[^abc]", x=x)
> [1] 1 2 3
> 
> But this is not what I want either.
> 
> I'd appreciate any help. I assume this is rather easy and
> straightforward.
> 
> Thanks,
> Roland
> 
> 
> [1] http://www.zytrax.com/tech/web/regex.htm: The ^ (circumflex or
> caret) inside square brackets negates the expression....
> 
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