Home R – is there a function similar to list.dirs which returns a named nested list instead of the character vector?

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R – is there a function similar to list.dirs which returns a named nested list instead of the character vector?

November 12, 2022

First let’s run this function to create the example folder structure:

c("Level1/Level1A/Level1AA", 
  "Level1/Level1A/Level1AB", 
  "Level1/Level1B/Level1BA", 
  "Level1/Level1B/Level1BB",
  "Level2/Level2A/Level2AA", 
  "Level2/Level2A/Level2AB", 
  "Level2/Level2B/Level2BA", 
  "Level2/Level2B/Level2BB") %>% 
  map(dir.create, recursive = T)

Now let’s imagine that this folder structure wasn’t created by R but given to us as is.

If I run list.dirs on the parent folder, I will get:

 [1] "."                         "./Level1"                  "./Level1/Level1A"          "./Level1/Level1A/Level1AA" "./Level1/Level1A/Level1AB"
 [6] "./Level1/Level1B"          "./Level1/Level1B/Level1BA" "./Level1/Level1B/Level1BB" "./Level2"                  "./Level2/Level2A"         
[11] "./Level2/Level2A/Level2AA" "./Level2/Level2A/Level2AB" "./Level2/Level2B"          "./Level2/Level2B/Level2BA" "./Level2/Level2B/Level2BB"

However, instead of this character vector, I wish to get a named nested list like this:

list(Level1 = list(Level1A = list("Level1AA",
                                  "Level1AB"),
                   Level1B = list("Level1BA",
                                  "Level1BB")),
     Level2 = list(Level2A = list("Level2AA",
                                  "Level2AB"),
                   Level2B = list("Level2BA",
                                  "Level2BB")))

What is the easiest way to achieve this?

>Solution :

You could use recursion in base R as follows:

my_fun <- function(x){
  ssplit <- function(x){
    if(is.data.frame(x))
      if(ncol(x)>1) c(by(x[-1], x[1], ssplit)) else as.list(x[[1]])
    else lapply(x, ssplit)
  }
  x <- grep("/", sub("^\\W+", "", x), value = TRUE)
  ssplit(read.table(text = x, sep='/', fill = TRUE, header = FALSE))
}

s <- c("Level1/Level1A/Level1AA", "Level1/Level1A/Level1AB", 
           "Level1/Level1B/Level1BA", "Level1/Level1B/Level1BB", "Level2/Level2A/Level2AA", 
           "Level2/Level2A/Level2AB", "Level2/Level2B/Level2BA",  "Level2/Level2B/Level2BB")

    my_fun(s)

$Level1
$Level1$Level1A
$Level1$Level1A[[1]]
[1] "Level1AA"

$Level1$Level1A[[2]]
[1] "Level1AB"


$Level1$Level1B
$Level1$Level1B[[1]]
[1] "Level1BA"

$Level1$Level1B[[2]]
[1] "Level1BB"



$Level2
$Level2$Level2A
$Level2$Level2A[[1]]
[1] "Level2AA"

$Level2$Level2A[[2]]
[1] "Level2AB"


$Level2$Level2B
$Level2$Level2B[[1]]
[1] "Level2BA"

$Level2$Level2B[[2]]
[1] "Level2BB"