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

Gabor Grothendieck ggrothendieck at gmail.com
Mon May 7 16:37:30 CEST 2007

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:
>   fixed: logical.  If 'TRUE', 'pattern' is a string to be matched as
>          is.  Overrides all conflicting arguments.
>   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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