Read all csv files in a directory and add the name of each file in a new column

Question

I have this code that reads all CSV files in a directory.

nm <- list.files()

df <- do.call(rbind, lapply(nm, function(x) read_delim(x,';',col_names = T)))

I want to modify it in a way that appends the filename to the data. The result would be a single data frame that has all the CSV files, and inside the data frame, there is a column that specifies from which file the data came. How to do it?

Answer 1

Instead of do.call(rbind, lapply(...)), you can use purrr::map_dfr() with the .id argument:

library(readr)
library(purrr)

df <- list.files() |>
  set_names() |>
  map_dfr(read_delim, .id = "file")

df

# A tibble: 9 × 3
  file    col1  col2
  <chr>  <dbl> <dbl>
1 f1.csv     1     4
2 f1.csv     2     5
3 f1.csv     3     6
4 f2.csv     1     4
5 f2.csv     2     5
6 f2.csv     3     6
7 f3.csv     1     4
8 f3.csv     2     5
9 f3.csv     3     6

Example data:

for (f in c("f1.csv", "f2.csv", "f3.csv")) {
  readr::write_delim(data.frame(col1 = 1:3, col2 = 4:6), f, ";")
}