On 11/03/2015 10:31, Bob O'Hara wrote:
Hi!
I'm trying to persuade R's regular expressions to do what I want. I
This is not "R's regular expressions" , but the world's regular expressions.
have a vector of strings which are names of variables, some of which
are elements of strings. I want to reformat all of the variables into
a list, so (for example) beta[1] and beta[2] would be a vector in the
list. Where I'm struggling is how to pick out the correct variables.
The problem is that if I have a sub-string, str, then I want to find
the strings that is either the same as the sub-string, or is the
substring followed by a '['. I feel I should be able to do this within
a character class if I could give it an end of string character, i.e.
'[$\\[]' where $ is not a literal $, but the end of the string (i.e.
how it's interpreted outside a character class)
$ inside a character class is a character, not a metacharacter.
Here's an example, using $ where I want the end of string:
VarNames <- c("alpha", "beta[1]", "beta[2]", "m", "mu.k", "mu.r")
TryNames <- unique(gsub('[]\\[1-9]',"",VarNames))
VarNames[grep(paste('^',TryNames[1], '[$\\[]', sep=""), VarNames)] # want
"alpha"
character(0)
VarNames[grep(paste('^',TryNames[2], '[$\\[]', sep=""), VarNames)] # Gives waht
I want
[1] "beta[1]" "beta[2]"
VarNames[grep(paste('^',TryNames[3], '[$\\[]', sep=""), VarNames)] # want "m"
character(0)
VarNames[grep(paste('^',TryNames[3], sep=""), VarNames)] # gives more than "m"
[1] "m" "mu.k" "mu.r"
Is it possible to do this, or will I have to resort to using '|'
(which works but is ugly & will only get uglier in the future)?
Why is
grep(paste0('^', TryNames[1], '($|\\[)'), VarNames, value = TRUE)
not a lot less ugly than the code you present?
Bob
--
Brian D. Ripley, rip...@stats.ox.ac.uk
Emeritus Professor of Applied Statistics, University of Oxford
1 South Parks Road, Oxford OX1 3TG, UK
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