Using an anonymous function in mutate - r

Question

I want to use the character strings from one column of a dataframe as the search string in a sub search of the character strings in another column of the dataframe on a row-by-row basis. I would like to do this using dplyr::mutate. I have figured out a way to do this using an anonymous function and apply, but I feel like apply shouldn't be necessary and I must be doing something wrong with how I'm implementing mutate. (And yes, I know that tools::file_path_sans_ext can give me the final result without needing to use mutate; I'm just want to understand how to use mutate.)
Here is the code that I think should work but doesn't:
files.vec <- dir(
dir.target,
full.names = T,
recursive = T,
include.dirs = F,
no.. = T
)
library(tools)
files.paths.df <- as.data.frame(
cbind(
path = files.vec,
directory = dirname(files.vec),
file = basename(files.vec),
extension = file_ext(files.vec)
)
)
library(tidyr)
library(dplyr)
files.split.df <- files.paths.df %>%
mutate(
no.ext = function(x) {
sub(paste0(".", x["extension"], "$"), "", x["file"])
}
)
| Error in mutate_impl(.data, dots) :
| Column `no.ext` is of unsupported type function
Here is the code that works, using apply:
files.split.df <- files.paths.df %>%
mutate(no.ext = apply(., 1, function(x) {
sub(paste0(".", x["extension"], "$"), "", x["file"])
}))
Can this be done without apply?

Answer 1

Apparently what you need is a whole bunch of parentheses. See https://stackoverflow.com/a/36906989/3277050
In your situation it looks like:
files.split.df <- files.paths.df %>%
mutate(
no.ext = (function(x) {sub(paste0(".", x["extension"], "$"), "", x["file"])})(.)
)
So it seems like if you wrap the whole function definition in brackets you can then treat it like a regular function and supply arguments to it.
New Answer
Really this is not the right way to use mutate at all though. I got focused in on the anonymous function part first without looking at what you are actually doing. What you need is a vectorized version of sub. So I used str_replace from the stringr package. Then you can just refer to columns by name because that is the beauty of dplyr:
library(tidyr)
library(dplyr)
library(stringr)
files.split.df <- files.paths.df %>%
mutate(
no.ext = str_replace(file, paste0(".", extension, "$"), ""))
Edit to Answer Comment
To use a user defined function where there isn't an existing vectorized function you could use Vectorize like this:
string_fun <- Vectorize(function(x, y) {sub(paste0(".", x, "$"), "", y)})
files.split.df <- files.paths.df %>%
mutate(
no.ext = string_fun(extension, file))
Or if you really don't want to name the function, which I do not recommend as it is much harder to read:
files.split.df <- files.paths.df %>%
mutate(
no.ext = (Vectorize(function(x, y) {sub(paste0(".", x, "$"), "", y)}))(extension, file))