Clash Royale CLAN TAG#URR8PPP

Extract substrings defined by positioning relative to other relatively positioned characters

I have many URLs in a character vector and I'm trying to extract substrings from them using base R. There are two types of substrings I want to extract:

I've hacked together a solution to this, but it involves many unecessary steps. Is there a way to accomplish this using a single regex per substring?

Below is my working example:

# An example URL
a <- "https://cran.r-project.org/src/contrib/Archive/ggplot2/ggplot2_0.4.5.tar.gz"

# Keep everything after the last slash
b <- sub('.*\/', '', a)
# Keep everything before .tar.gaz
c <- sub('.tar.*', '', b)

# Extract desired strings based on underscore
foo <- sub('.*\_', '', c)
bar <- sub('\_.*', '', c)


It is important for this example to use base R.

sub(".tar.*", "", strsplit(basename(a), "_")[[1]])

3 Answers
3

Solution that uses basename and strsplit at _:

basename

strsplit

_

sub(".tar.*", "", strsplit(basename(a), "_")[[1]])
[1] "ggplot2" "0.4.5"


Using lookarounds:

regmatches(a, regexpr('(?<=\/)[^\/]+(?=_)', a, perl = T))
[1] "ggplot2"
regmatches(a, regexpr('(?<=_)[^_]+(?=\.tar\.gz)', a, perl = T))
[1] "0.4.5"


Try this pattern: /(?<package>[^/]+)_(?<version>[^_/]+).tar.gz$.

/(?<package>[^/]+)_(?<version>[^_/]+).tar.gz$

In a match, first capturing group, named package will give you The substring after the last slash (/) in the string and before the last underscore (_) and second, named version, will give you The substring after the last underscore (_) and before the substring .tar.gz.

package

version

Demo

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