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I run
dir.create('./junk_data')
file.create(paste('./junk_data/QWE',01:12,01:31,2005:2015,'.3',sep=''))
file.create(paste('./junk_data/RTY',01:12,01:31,2005:2015,'.3',sep=''))
and want to list all the files that begin with QWE and end with 2011.3. I tried
list.files('./junk_data/',pattern='QWE....2011.3',full.names=T)
and
list.files('./junk_data/',pattern='QWE....2011.3',full.names=T,perl=T)
but I guess '.' doesn't mean one what I think, as I get none of the files I want.
I tried a few tutorials on regex, but no joy.
948
To list all files in a directory in R programming language we use list. files(). This function produces a list containing the names of files in the named directory. It returns a character vector containing the names of the files in the specified directories.
Two types of regular expressions are used in R, extended regular expressions (the default) and Perl-like regular expressions used by perl = TRUE . There is also fixed = TRUE which can be considered to use a literal regular expression.
Placing r or R before a string literal creates what is known as a raw-string literal. Raw strings do not process escape sequences ( \n , \b , etc.) and are thus commonly used for Regex patterns, which often contain a lot of \ characters.
As Arun showed in his example, a dot usually means "match any character", so to match a dot you need to escape it: \\.. You can create the pattern most easily with glob2rx, which uses * as a wildcard and matches other characters as though they are fixed.
glob2rx("QWE*2011.3") #"^QWE.*2011\\.3$"
list.files("./junk_data/", pattern = glob2rx("QWE*2011.3"), full.names = TRUE)
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