forked from tidyverse/readr
-
Notifications
You must be signed in to change notification settings - Fork 0
/
README.Rmd
147 lines (103 loc) · 5.61 KB
/
README.Rmd
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
---
output: github_document
---
<!-- README.md is generated from README.Rmd. Please edit that file -->
```{r setup, include = FALSE}
knitr::opts_chunk$set(
collapse = TRUE,
comment = "#>",
fig.path = "man/figures/README-"
)
```
# readr <a href="https://readr.tidyverse.org"><img src="man/figures/logo.png" align="right" height="139" /></a>
[](https://cran.r-project.org/package=readr)
[](https://travis-ci.org/tidyverse/readr)
[](https://ci.appveyor.com/project/tidyverse/readr)
[](https://codecov.io/gh/tidyverse/readr?branch=master)
## Overview
The goal of readr is to provide a fast and friendly way to read rectangular data (like csv, tsv, and fwf). It is designed to flexibly parse many types of data found in the wild, while still cleanly failing when data unexpectedly changes. If you are new to readr, the best place to start is the [data import chapter](http://r4ds.had.co.nz/data-import.html) in R for data science.
## Installation
```{r, eval = FALSE}
# The easiest way to get readr is to install the whole tidyverse:
install.packages("tidyverse")
# Alternatively, install just readr:
install.packages("readr")
# Or the the development version from GitHub:
# install.packages("devtools")
devtools::install_github("tidyverse/readr")
```
## Cheatsheet
<a href="https://rawgit.com/rstudio/cheatsheets/master/data-import.pdf"><img src="https://raw.githubusercontent.com/rstudio/cheatsheets/master/pngs/thumbnails/data-import-cheatsheet-thumbs.png" width="630" height="252"/></a>
## Usage
readr is part of the core tidyverse, so load it with:
```{r}
library(tidyverse)
```
To accurately read a rectangular dataset with readr you combine two pieces: a function that parses the overall file, and a column specification. The column specification describes how each column should be converted from a character vector to the most appropriate data type, and in most cases it's not necessary because readr will guess it for you automatically.
readr supports seven file formats with seven `read_` functions:
* `read_csv()`: comma separated (CSV) files
* `read_tsv()`: tab separated files
* `read_delim()`: general delimited files
* `read_fwf()`: fixed width files
* `read_table()`: tabular files where columns are separated by white-space.
* `read_log()`: web log files
In many cases, these functions will just work: you supply the path to a file and you get a tibble back. The following example loads a sample file bundled with readr:
```{r}
mtcars <- read_csv(readr_example("mtcars.csv"))
```
Note that readr prints the column specification. This is useful because it allows you to check that the columns have been read in as you expect, and if they haven't, you can easily copy and paste into a new call:
```{r, eval = FALSE}
mtcars <- read_csv(readr_example("mtcars.csv"), col_types =
cols(
mpg = col_double(),
cyl = col_integer(),
disp = col_double(),
hp = col_integer(),
drat = col_double(),
vs = col_integer(),
wt = col_double(),
qsec = col_double(),
am = col_integer(),
gear = col_integer(),
carb = col_integer()
)
)
```
`vignette("readr")` gives more detail on how readr guesses the column types, how you can override the defaults, and provides some useful tools for debugging parsing problems.
## Alternatives
There are two main alternatives to readr: base R and data.table's `fread()`. 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_names` and
`col_types` not `header` and `colClasses`).
* Are much faster (up to 10x).
* Leave strings as is by default, and automatically parse common
date/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 current locale.
To override the US-centric defaults, use `locale()`.
### data.table and `fread()`
[data.table](https://github.com/Rdatatable/data.table) has a function similar to `read_csv()` called fread. Compared to fread, readr functions:
* Are slower (currently ~1.2-2x slower. If you want absolutely the best
performance, use `data.table::fread()`.
* Use a slightly more sophisticated parser, recognising both
doubled (`""""`) and backslash escapes (`"\""`), and can produce
factors and date/times directly.
* Forces you to supply all parameters, where `fread()` saves you work by
automatically guessing the delimiter, whether or not the file has a
header, and how many lines to skip.
* Are built on a different underlying infrastructure. Readr functions
are designed to be quite general, which makes it easier to add
support for new rectangular data formats. `fread()` is designed to be
as fast as possible.
## Acknowledgements
Thanks to:
* [Joe Cheng](https://github.com/jcheng5) for showing me the beauty of
deterministic finite automata for parsing, and for teaching me why I
should write a tokenizer.
* [JJ Allaire](https://github.com/jjallaire) for helping me come up with a
design that makes very few copies, and is easy to extend.
* [Dirk Eddelbuettel](http://dirk.eddelbuettel.com) for coming up with the
name!
Please note that this project is released with a [Contributor Code of Conduct](CONDUCT.md).
By participating in this project you agree to abide by its terms.