[R] Pattern Matching help

[Uwe Ligges]

Samir Mishra wrote:
> 
> Thanks in advance for any help I can get on this.
> 
> I'm trying to change variable names between 2 systems - R and old SPSS,
> Oracle. I'm using the grep() and gsub() commands but I'm getting the
> following result -
> 
> > test.dat <- c("a", "b.c", "d.e.f", "p_q,r")
> 
> > test.dat
> [1] "a"     "b.c"   "d.e.f" "p_q,r"
> 
> > grep(",", test.dat, value = TRUE, extended = FALSE)
> [1] "p_q,r"
> 
> > grep("_", test.dat, value = TRUE, extended = FALSE)
> [1] "p_q,r"
> 
> > #NOT WHAT I WANT, I EXPECT TO GET ONLY ELEMENTS 2 & 3 RETURNED
> > grep(".", test.dat, value = TRUE, extended = FALSE)
> [1] "a"     "b.c"   "d.e.f" "p_q,r"

grep("\\.", test.dat, value = TRUE, extended = FALSE)


> And similarly, with gsub(), I get -
> > gsub(",", "_", test.dat, extended = FALSE)
> [1] "a"     "b.c"   "d.e.f" "p_q_r"
> 
> > gsub("_", ".", test.dat, extended = FALSE)
> [1] "a"     "b.c"   "d.e.f" "p.q,r"
> 
> > #NOT WHAT I WANT
> > gsub(".", "_", test.dat, extended = FALSE) #NOT WHAT I WANT
> [1] "_"     "___"   "_____" "_____"

gsub("\\.", "_", test.dat, extended = FALSE)


> Am I doing something wrong?


Yes. Think about the "." in regular expressions.

Uwe Ligges
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