regex -> negate a word

Thanks! (I have to admit, though, that I expected something simple)

Thanks,
Roland



-----Original Message-----
From: Gabor Grothendieck [mailto:ggrothendieck at gmail.com]
Sent: Sun 1/18/2009 8:54 PM
To: Rau, Roland
Cc: r-help at r-project.org
Subject: Re: [R] regex -> negate a word

Try this:

grep("^([^a]|a[^b]|ab[^c])*.{0,2}$", x, perl = TRUE)


On Sun, Jan 18, 2009 at 2:37 PM, Rau, Roland <Rau at demogr.mpg.de> wrote:

Thank you very much to all of you for your fast and excellent help.
Since the "-grep(...)" solution seems to be favored by most of the
answers,
I just wonder if there is really no regular expression which does the
job?!?

Thanks again,
Roland



-----Original Message-----
From: Gabor Grothendieck [mailto:ggrothendieck at gmail.com]
Sent: Sun 1/18/2009 8:28 PM
To: Rau, Roland
Cc: r-help at r-project.org
Subject: Re: [R] regex -> negate a word

Try this:

# indexes
setdiff(seq_along(x), grep("abc", x))

# values
setdiff(x, grep("abc", x, value = TRUE))

Another possibility is:

z <- "abc"
x0 <- c(x, z) # to handle no match case
x0[- grep(z, x0)] # values




On Sun, Jan 18, 2009 at 1:35 PM, Rau, Roland <Rau at demogr.mpg.de> 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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