Re: [Rd] grep with fixed=TRUE and ignore.case=TRUE

From: Gabor Grothendieck <ggrothendieck_at_gmail.com>
Date: Mon, 07 May 2007 10:37:30 -0400

Seems like a good idea to me.

Here is a workaround that works in any event which combines (?i), \Q and \E . to get the same effect. (?i) gives case insensitive matches and \Q and \E quote and endquote the intervening text disabling special characters:

x <- c("D.G cat", "d.g cat", "dog cat")
z <- "d.g"

rx <- paste("(?i)\\Q", z, "\\E", sep = "") grep(rx, x, perl = TRUE) # 1 2

On 5/7/07, Petr Savicky <savicky_at_cs.cas.cz> wrote:
> Dear R developers,
>
> I suggest to modify the behaviour of "grep" function with fixed=TRUE option.
>
> Currently, fixed=TRUE implies ignore.case=FALSE (overrides ignore.case=TRUE,
> if set by the user).
>
> I suggest to keep ignore.case as set by the user even if fixed=TRUE. Since
> the default of ignore.case is FALSE, this would not change the behaviour
> of grep, if the user does not set ignore.case explicitly.
>
> In my opinion, fixed=TRUE is most useful for suppressing meta-character
> expansion. On the other hand, for a simple word search, ignoring
> case is sometimes useful.

>
> If for some reason, it is better to keep the current behavior of grep, then I
> suggest to extend the documentation as follows:
>
> ORIGINAL:
> fixed: logical. If 'TRUE', 'pattern' is a string to be matched as
> is. Overrides all conflicting arguments.
>
> SUGGESTED:
> fixed: logical. If 'TRUE', 'pattern' is a string to be matched as
> is. Overrides all conflicting arguments including ignore.case.
>
> All the best, Petr Savicky.
>
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>



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