R - how to extract a string between two delimiters when there are multiple instances of the same delimiter

Question

some previous questions have been asked on this topic, but they don't seem to include the case when a string contains multiple instances of the same delimiter.

How to extract substring between patterns "_" and "." in R

Extracting a string between other two strings in R

Extract a string between patterns/delimiters in R

The problem I am facing is the following. Say we have a vector like this:

vec <- c("Europe/Germany/Berlin/Mitte", 
         "Europe/Germany/Berlin/Charlottenburg", 
         "Europe/Croatia/Zagreb/Gornji Grad", 
         "Europe/Croatia/Zagreb/Donji Grad")

Can you provide me with the following two functions:

The output of the first function should be:

c("Germany", "Germany", "Croatia", "Croatia")

And the output of the second function should be:

c("Berlin", "Berlin", "Zagreb", "Zagreb")

I don't understand how the answers from previous questions apply when the delimiter / appears more than once in the string and how can I specify which of the pieces I want.

Answer 1

We can try using sapply() along with strsplit() here for a base R solution:

unname(sapply(vec, function(x) unlist(strsplit(x, "/"))[2]))

[1] "Germany" "Germany" "Croatia" "Croatia"

unname(sapply(vec, function(x) unlist(strsplit(x, "/"))[3]))

[1] "Berlin" "Berlin" "Zagreb" "Zagreb"

Answer 2

library(tidyverse)

get_name <- function(position) {
  vec %>%
    str_split("/") %>%
    map_chr( ~ .x[position])
}

Get position 2

get_name(2)
[1] "Germany" "Germany" "Croatia" "Croatia"

Get position 3

get_name(3)
[1] "Berlin" "Berlin" "Zagreb" "Zagreb"

Answer 3

Here is another option. When you have a structured text like this, you can create four capture groups to encompass the text between the back slashes, then you can call the captured text by group:

vec <- c("Europe/Germany/Berlin/Mitte", 
         "Europe/Germany/Berlin/Charlottenburg", 
         "Europe/Croatia/Zagreb/Gornji Grad", 
         "Europe/Croatia/Zagreb/Donji Grad")

rgx <- "(.*)/(.*)/(.*)/(.*)"

sub(rgx, "\\1", vec)
#> [1] "Europe" "Europe" "Europe" "Europe"
sub(rgx, "\\2", vec)
#> [1] "Germany" "Germany" "Croatia" "Croatia"
sub(rgx, "\\3", vec)
#> [1] "Berlin" "Berlin" "Zagreb" "Zagreb"
sub(rgx, "\\4", vec)
#> [1] "Mitte"          "Charlottenburg" "Gornji Grad"    "Donji Grad"