I have an example where escaping "." does not seem to be behaving
consistently, but perhaps it is due to my misunderstanding. Could someone
explain to me why the below produces the output it does?

It seems to me that in the second example, where I am being more precise
about specifying that a "." (dot) should be between the numbers, should
produce the same output as the first example, but it does not.

As an aside, is there a document or help page that specifies which
characters need to be escaped to form regex's in R? I can't find one.

Finally, how does one grep for the escape character? I've tried
   grep ("\\", vector)
   grep ("\\\", vector)
   grep("\\\\", vector)
all without success.

Thanks, Mark

a <- "160.15.05.00"
grep("[1-9]+.[0-9]+\\.[0-9]+\\.[0-0]+", a)
# [1]
grep("[1-9]+\\.[0-9]+\\.[0-9]+\\.[0-0]+", a)
# integer(0)

> sessionInfo()
R version 2.11.0 Under development (unstable) (2009-12-28 r50849)
x86_64-unknown-linux-gnu

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C
 [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8
 [5] LC_MONETARY=C              LC_MESSAGES=en_US.UTF-8
 [7] LC_PAPER=en_US.UTF-8       LC_NAME=C
 [9] LC_ADDRESS=C               LC_TELEPHONE=C
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C

attached base packages:
[1] grid      stats     graphics  grDevices datasets  utils     methods
[8] base

other attached packages:
[1] Rgraphviz_1.25.1 graph_1.25.4

loaded via a namespace (and not attached):
[1] tools_2.11.0

Mark W. Kimpel MD  ** Neuroinformatics ** Dept. of Psychiatry
Indiana University School of Medicine

15032 Hunter Court, Westfield, IN  46074

(317) 490-5129 Work, & Mobile & VoiceMail
(317) 399-1219 Skype No Voicemail please

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