How to read multiple csv files into a single data frame in R?

Question

How to read multiple csv files into a single data frame in R?

Similar questions have been asked here:

• Read multiple CSV files into separate data frames most answers use the assign() function to assign to many data frames.
• How do I make a list of data frames? most answers add data frames to a list of data frames using append(l, df) or l[[i]]=df.

Reproducible example

Write sample csv files to a temporary directory.

library(dplyr)
library(tidyr)
library(purrr)
library(purrrlyr)
library(readr)
data_dir <- file.path(tempdir(), "iris")
dir.create(data_dir)
iris %>%
    # To keep the Species column in the output
    # Create a new column that will be used as the grouping variable
    mutate(species_group = Species) %>%
    group_by(species_group) %>%
    nest() %>%
    # Apply the write.csv() function to each row of the nested data frame
    by_row(~write.csv(.$data,
                      file = file.path(data_dir, paste0(.$species_group, ".csv")),
                      row.names = FALSE))

In this example, there are 3 .csv files in the data_dir. The question is how to read them all into a single data frame.

Answer 1

To read many csv files into one data frame:

1. Lists files with their full path.
2. Apply the read_csv function to each element of the vector of file paths and return a data frame created by row-binding.

iris_csv <- list.files(data_dir, full.names = TRUE) %>%
    map_dfr(read_csv)