On Jan 7, 2010, at 2:47 PM, Mark Kimpel wrote:
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.
there is an intervening "0" in between the matching 1-9 group and the
first period causing a pattern failure for match of "160." with "[1-9]+
\\."
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.
?regex # what else?
Finally, how does one grep for the escape character? I've tried
grep ("\\", vector)
grep ("\\\", vector)
grep("\\\\", vector)
Where or perhaps what is "vector"? Why should we think it has an
"escape character" in it? In some sense I think you have an
epistemological problem. There can be back-slashes in strings, but
they are not escape characters at that point.
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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