How to Get Extension of a File in R

If you want to put data validation in progress, you must identify the file type or “MIME Type” before processing. To identify the file type, we might need to check its extension.

Here are two ways to get an extension of a file in R:

1. Using the tools::file_ext()
2. Using regular expression

Method 1: Using the tools::file_ext()

The file_ext() is not a base R’s but a “tools” package’s method. It accepts “file path” and returns only the extension of the file.

We must install the package if we have to use it.

install.packages("tools")

Load the package like this:

library("tools")

Visual representation

Before getting the extension of a file, you need to check if a file exists.

Use the file.exists() method to check for a file’s existence. If it exists, you can use the file_ext() function.

Example

library(tools)

file <- "dataframe.R"

if (file.exists(file)) {

  file_ext(file)

} else {

  cat("The file does not exist")

}

Output

[1] "R"

Method 2: Using regular expression

If you are not keen on using third-party packages, then old ways to use “Regular Expressions”.  R provides a sub() or gsub() method to create a regex pattern to help us extract extension from the file name.

Example

file <- "dataframe.R"

extension <- sub(".*\\.", "", file)

print(extension)

Output

[1] "R"

Getting a filename without an extension

If you have a requirement to extract a filename without extension, you can use the “file_path_sans_ext()” method. Unfortunately, the file_path_sans_ext() method is not a built-in method, and you also have to install and import the “tools” package first.

Example

library(tools)

file <- "dataframe.R"

if (file.exists(file)) {

  file_path_sans_ext(file)

} else {

  cat("The file does not exist")

}

Output

[1] "dataframe"

You can also use the basename() function to remove the path leading to the file, and with this regex, any extension will be removed.

library(tools)

file <- "dataframe.R"

if (file.exists(file)) {

  sub(pattern = "(.*)\\..*$", replacement = "\\1", basename(file))

} else {

  cat("The file does not exist")

}

Output

[1] "dataframe"

That is it.