String Pattern in R - r

Question

I have a list of strings as follow: "/home/ricardo/MultiClass/data//F10/1036.txt"
> library(stringr)
> strsplit(cls[1], split= "/")
Give me:
#> [[1]] [1] "" "home" "ricardo" "MultiClass" "data"
#> "" "F10" "1036.txt"
How can I keep only the 7th position?
#> "F10"

Answer 1

If you want to extract one or more chars after // up to the first / or end of string use
> library(stringr)
> s <- "/home/ricardo/MultiClass/data//F10/1036.txt"
> str_extract(s, "(?<=//)[^/]+")
[1] "F10"
The (?<=//)[^/]+ regex pattern will find a position that is preceded with 2 slashes (see (?<=//)) and then matches one or more characters other than / (see [^/]+).
A base R solution with sub will look like
> sub("^.*/([^/]*)/[^/]*$", "\\1", s)
[1] "F10"
Details:
^ - start of string
.* - any 0+ chars as many as possible
/ - a slash (last but one in the string as the previous pattern is greedy)
([^/]*) - capturing group #1 matching any 0+ chars other than /
/ - last slash
[^/]* - any 0+ chars other than /
$ - end of string.

Answer 2

Using function word of stringr,
library(stringr)
word(sub('.*//', '', s), 1, sep = '/')
#[1] "F10"
#where
s <- '/home/ricardo/MultiClass/data//F10/1036.txt'

Answer 3

It can be done in R-base in this way.
I have defined the function gret to extract a pattern from a string
gret <-function(pattern,text,ignore.case=TRUE){
regmatches(text,regexpr(pattern,text,perl=TRUE,ignore.case))
then
gsub("data|/*","",gret("(?=data/).*(?<=/)","/home/ricardo/MultiClass
/data//F10/1036.txt"))
#>[1] "F10"