# Input and output

# Reading and writing data frames

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:

# Remarks

To construct file paths, for reading or writing, use file.path.

Use dir to see what files are in a directory.