5.1 Exporting Data to Delimited Files

We will start by introducing how to export data to a file in this chapter.

5.1.1 Set the working directory

First, we will introduce an important concept called Working Directory. To do data export and import, you are recommended to set the working directory since we usually use a path relative to the working directory for interacting with files on the computer in R. To set the working directory, you can click Session on the menu and click Set Working Directory.

Set Working Directory

Figure 5.1: Set Working Directory

There are three options under this menu.

  • To Source File Location: this is the same directory as the current R script.
  • To Files Pane Location: this is the same directory as shown in the Files Panel on the bottom right of RStudio.
  • Choose Directory…: this will open up a window from which you can choose any desired directory.
After selecting any of the three options, we can see a line of code containing the function setwd() executed in the console.
Set Working Directory (2)

Figure 5.2: Set Working Directory (2)

Indeed, this menu operation is equivalent to using the setwd() function with the argument being the full path or relative path of the desired directory.

Another related function is getwd() which tells us the absolute path representing the current working directory.

getwd()

5.1.2 Delimited files

In most applications, you will use a specific file type called delimited file. In a delimited file, each row represents a single observation, and it has values separated by the delimiter. In principle, any character (including letters, numbers, or symbols) can be used as a delimiter, with the most commonly used ones being the following.

Delimiter Symbol Common File Extension
comma , .csv
space .txt
tab \t .tsv

5.1.3 Write an object into a .csv file

First, let’s work with one popular kind of delimited files called comma-separated value file, usually with the file extension .csv. In a .csv file, the delimiter is comma (,) .

Let’s first create a data frame.

dig_num <- 7:1
ani_char <- c("sheep", "pig", "monkey", "pig", "monkey", NA, "pig")
conditions <- c("Excellent", "Good", "N", "Fair", "Good", "Good", "Excellent")
my_animals<- data.frame(dig_num, ani_char, conditions)
my_animals

Now, let’s write the data frame my_animals into a file called “my_animals.csv” in the currently working directory. To write an object into a .csv file, you can use the write_csv() function in the readr package. Since readr is a sub-package of tidyverse, you can load the package directly if the tidyverse package is installed.

library(readr)
write_csv(my_animals, "my_animals.csv")

You can verify the .csv file has been indeed created and open the file with RStudio or any text editor to verify its contents.

File Contents

Figure 5.3: File Contents

We can see that all the information has been written in the .csv file, which has commas separating the values on each line. In particular, you may find out the first row of the file corresponds to the column names. If you don’t want to include the column names, you can set the argument col_names = FALSE.

write_csv(my_animals, "my_animals_no_colname.csv", col_names = FALSE)

By default, write_csv() writes the data into a file in which NA is used to represent all the missing values, just like in the tibble. If you want to use another string to represent the missing values in the file, you can set the argument na to be the string.

write_csv(my_animals, "my_animals_missing.csv", na = "This value is missing!")

5.1.4 Write an object into a general delimited file

As introduced at the beginning, there are different types of delimited files depending on the specific delimiter. The function write_delim() enables us to write an object into a delimited file with any chosen delimiter. The usage of write_delim() is almost identical to write_csv(), except that it has an additional argument delim, which specifies the delimiter to be used. Let’s see the following example with * as the delimiter.

write_delim(my_animals, "my_animals_star.csv", delim = "*")

5.1.5 Exercises

Use R to create the following data frame and assign it to the name my_data.

#>   word number letter
#> 1  one      1      a
#> 2  two     NA      b
#> 3 <NA>      3      c
#> 4 four      4      d
#> 5 five      5      e

  1. Write R code to set working directory to the location of your .R or .Rmd file, and export my_data into a .csv file named “my_data_no_name.csv” without column names.

  2. Write R code to export my_data into a delimited file called “my_data_na.csv” with # as the delimiter and use 999 as the indicator for missing values.