readr package - RDocumentation (2024)

Overview

The goal of readr is to provide a fast and friendly way to readrectangular data from delimited files, such as comma-separated values(CSV) and tab-separated values (TSV). It is designed to parse many typesof data found in the wild, while providing an informative problem reportwhen parsing leads to unexpected results. If you are new to readr, thebest place to start is the data importchapter in R for Data Science.

Installation

# The easiest way to get readr is to install the whole tidyverse:install.packages("tidyverse")# Alternatively, install just readr:install.packages("readr")

# Or you can install the development version from GitHub:# install.packages("pak")pak::pak("tidyverse/readr")

Cheatsheet

Usage

readr is part of the core tidyverse, so you can load it with:

library(tidyverse)#> ── Attaching core tidyverse packages ──────────────────────── tidyverse 2.0.0 ──#> ✔ dplyr 1.1.4 ✔ readr 2.1.4.9000#> ✔ forcats 1.0.0 ✔ stringr 1.5.1 #> ✔ ggplot2 3.4.3 ✔ tibble 3.2.1 #> ✔ lubridate 1.9.3 ✔ tidyr 1.3.0 #> ✔ purrr 1.0.2 #> ── Conflicts ────────────────────────────────────────── tidyverse_conflicts() ──#> ✖ dplyr::filter() masks stats::filter()#> ✖ dplyr::lag() masks stats::lag()#> ℹ Use the conflicted package (<http://conflicted.r-lib.org/>) to force all conflicts to become errors

Of course, you can also load readr as an individual package:

library(readr)

To read a rectangular dataset with readr, you combine two pieces: afunction that parses the lines of the file into individual fields and acolumn specification.

readr supports the following file formats with these read_*()functions:

read_csv(): comma-separated values (CSV)
read_tsv(): tab-separated values (TSV)
read_csv2(): semicolon-separated values with , as the decimal mark
read_delim(): delimited files (CSV and TSV are important specialcases)
read_fwf(): fixed-width files
read_table(): whitespace-separated files
read_log(): web log files

A column specification describes how each column should be convertedfrom a character vector to a specific data type (e.g.character,numeric, datetime, etc.). In the absence of a column specification,readr will guess column types from the data. vignette("column-types")gives more detail on how readr guesses the column types. Column typeguessing is very handy, especially during data exploration, but it’simportant to remember these are just guesses. As any data analysisproject matures past the exploratory phase, the best strategy is toprovide explicit column types.

The following example loads a sample file bundled with readr and guessesthe column types:

(chickens <- read_csv(readr_example("chickens.csv")))#> Rows: 5 Columns: 4#> ── Column specification ────────────────────────────────────────────────────────#> Delimiter: ","#> chr (3): chicken, sex, motto#> dbl (1): eggs_laid#> #> ℹ Use `spec()` to retrieve the full column specification for this data.#> ℹ Specify the column types or set `show_col_types = FALSE` to quiet this message.#> # A tibble: 5 × 4#> chicken sex eggs_laid motto #> <chr> <chr> <dbl> <chr> #> 1 Foghorn Leghorn rooster 0 That's a joke, ah say, that's a jok…#> 2 Chicken Little hen 3 The sky is falling! #> 3 Ginger hen 12 Listen. We'll either die free chick…#> 4 Camilla the Chicken hen 7 Bawk, buck, ba-gawk. #> 5 Ernie The Giant Chicken rooster 0 Put Captain Solo in the cargo hold.

Note that readr prints the column types – the guessed column types, inthis case. This is useful because it allows you to check that thecolumns have been read in as you expect. If they haven’t, that means youneed to provide the column specification. This sounds like a lot oftrouble, but luckily readr affords a nice workflow for this. Usespec() to retrieve the (guessed) column specification from yourinitial effort.

spec(chickens)#> cols(#> chicken = col_character(),#> sex = col_character(),#> eggs_laid = col_double(),#> motto = col_character()#> )

Now you can copy, paste, and tweak this, to create a more explicit readrcall that expresses the desired column types. Here we express that sexshould be a factor with levels rooster and hen, in that order, andthat eggs_laid should be integer.

chickens <- read_csv( readr_example("chickens.csv"), col_types = cols( chicken = col_character(), sex = col_factor(levels = c("rooster", "hen")), eggs_laid = col_integer(), motto = col_character() ))chickens#> # A tibble: 5 × 4#> chicken sex eggs_laid motto #> <chr> <fct> <int> <chr> #> 1 Foghorn Leghorn rooster 0 That's a joke, ah say, that's a jok…#> 2 Chicken Little hen 3 The sky is falling! #> 3 Ginger hen 12 Listen. We'll either die free chick…#> 4 Camilla the Chicken hen 7 Bawk, buck, ba-gawk. #> 5 Ernie The Giant Chicken rooster 0 Put Captain Solo in the cargo hold.

vignette("readr") gives an expanded introduction to readr.

Editions

readr got a new parsing engine in version 2.0.0 (released July 2021). Inthis so-called second edition, readr calls vroom::vroom(), by default.

The parsing engine in readr versions prior to 2.0.0 is now called thefirst edition. If you’re using readr >= 2.0.0, you can still accessfirst edition parsing via the functions with_edition(1, ...) andlocal_edition(1). And, obviously, if you’re using readr < 2.0.0, youwill get first edition parsing, by definition, because that’s all thereis.

Alternatives

There are two main alternatives to readr: base R and data.table’sfread(). The most important differences are discussed below.

Base R

Compared to the corresponding base functions, readr functions:

Use a consistent naming scheme for the parameters (e.g.col_namesand col_types not header and colClasses).
Are generally much faster (up to 10x-100x) depending on the dataset.
Leave strings as is by default, and automatically parse commondate/time formats.
Have a helpful progress bar if loading is going to take a while.
All functions work exactly the same way regardless of the currentlocale. To override the US-centric defaults, use locale().

data.table and `fread()`

data.table has a functionsimilar to read_csv() called fread(). Compared to fread(), readrfunctions:

Are sometimes slower, particularly on numeric heavy data.
Can automatically guess some parameters, but basically encourageexplicit specification of, e.g., the delimiter, skipped rows, and theheader row.
Follow tidyverse-wide conventions, such as returning a tibble, astandard approach for column name repair, and a common mini-languagefor column selection.

Acknowledgements

Thanks to:

Joe Cheng for showing me the beauty ofdeterministic finite automata for parsing, and for teaching me why Ishould write a tokenizer.
JJ Allaire for helping me come up witha design that makes very few copies, and is easy to extend.
Dirk Eddelbuettel for coming up withthe name!