R function to get directory name of a file as characters - r

Question

I can create a list of csv files in folder_A:
list1 <- dir_ls("path to folder_A")
I can define a function to add a column with filenames and combine these files into one dataframe:
read_and_save_combo <- function(fileX){
read_csv(fileX) %>%
mutate(fileX = path_file(fileX)}
combo_df <- map_df(list1, read_and_save_combo)
I want to add another column with enclosing folder name (would be the same for all files, folder_A). If I use dirname() on an individual file, I get the full parent directory path to folder_A. I only want the characters "folder_A". If I use dirname() as part of the function, I get another column but its filled with "." Less importantly, I don't know why I get the "." instead of the full path, but more importantly is there a function like path_parentfoldername, that would let me add a new column with only the name of the folder containing each file to each row of the combined dataframe?
Thanks!
Edit:
New function for clarity after answers:
read_and_save_combo <- function(fileX){
read_csv(fileX) %>%
mutate(filename = path_file(fileX), foldername = dirname(fileX) %>%
str_replace(pattern = ".*/", replacement = ""))}
This works because . is the wildcard but * modifies the meaning to 0-infinity characters, so ".*" is any character and any number of characters preceding /. Gregor said this but now I understand it.
Also, I was getting the column filled with ".", because in the function, I was reading one file, but then trying to mutate with dirname operating on the list, which is a vector with multiple elements (more than one file).

Answer 1

You can use dirname + basename :
list1 <- list.files('folder_A_path', full.names = TRUE)
read_and_save_combo <- function(fileX) {
readr::read_csv(fileX) %>%
dplyr::mutate(fileX = basename(dirname(fileX)))
}
combo_df <- purrr::map_df(list1, read_and_save_combo)
If your file is at the path 'Users/Downloads/FolderA/Filename.csv' :
dirname('Users/Downloads/FolderA/Filename.csv')
#[1] "Users/Downloads/FolderA"
basename(dirname('Users/Downloads/FolderA/Filename.csv'))
#[1] "FolderA"

Answer 2

"path to folder_A" is a bad example, use "path/to/folder_A". You need to delete everything from the start through the last /:
library(stringr)
str_replace("path/to/folder_A", pattern = ".*/", replacement = "")
# [1] "folder_A"
If you're worried about \\ or other non-standard things, use dirname() as the input.

Answer 3

Here are two ways to do what I wanted, using the helpful answers above:
read_and_save_combo <- function(file){
read_csv(file) %>%
mutate(filename = path_file(file), foldername = basename(dirname(file)))}
read_and_save_combo <- function(file){
read_csv(file) %>%
mutate(filename = path_file(file), foldername = dirname(file) %>%
str_replace(pattern = ".*/", replacement = ""))}
Other basic things I learned that could be helpful for other beginners:
(1) While writing the function, point all the functions (read_csv(), dirname(), etc.) at a uniform variable (here written as "file" but it could be just a letter "g" or whatever you choose). Then you will avoid the problem I had where part of the function is acting on one file and another part is acting on a list.
(2)
filex and fileX
appear far too similar to each other using certain fonts, which can mess you up (capitalization).