R Language Input and output Reading and writing data frames
Example
Data frames are R's tabular data structure. They can be written to or read from in a variety of ways.
This example illustrates a couple common situations. See the links at the end for other resources.
Writing
Before making the example data below, make sure you're in a folder you want to write to. Run getwd() to verify the folder you're in and read ?setwd if you need to change folders.
set.seed(1)
for (i in 1:3)
write.table(
data.frame(id = 1:2, v = sample(letters, 2)),
file = sprintf("file201%s.csv", i)
)
Now, we have three similarly-formatted CSV files on disk.
Reading
We have three similarly-formatted files (from the last section) to read in. Since these files are related, we should store them together after reading in, in a list:
file_names = c("file2011.csv", "file2012.csv", "file2013.csv")
file_contents = lapply(setNames(file_names, file_names), read.table)
# $file2011.csv
# id v
# 1 1 g
# 2 2 j
#
# $file2012.csv
# id v
# 1 1 o
# 2 2 w
#
# $file2013.csv
# id v
# 1 1 f
# 2 2 w
To work with this list of files, first examine the structure with str(file_contents), then read about stacking the list with ?rbind or iterating over the list with ?lapply.
Further resources
Check out ?read.table and ?write.table to extend this example. Also:
- R binary formats (for tables and other objects)
- Plain-text table formats
- comma-delimited CSVs
- tab-delimited TSVs
- Fixed-width formats
- Language-agnostic binary table formats
- Feather
- Foreign table and spreadsheet formats
- SAS
- SPSS
- Stata
- Excel
- Relational database table formats
- MySQL
- SQLite
- PostgreSQL
