What is the fastest, most optimized, one-liner way to get an array of the directories (excluding files) in Ruby?

Fastest and Most Optimized One-Liner to Get Directories in Ruby

In Ruby, retrieving an array of directories (excluding files) within a specific path can be achieved efficiently using a one-liner. The most optimized approach leverages the Dir.children method combined with select to filter out only directories. This method is both concise and performant, making it ideal for quick directory listings.

One-Liner Solution:

directories = Dir.children(path).select { |entry| File.directory?(File.join(path, entry)) }

Explanation:

1. Dir.children(path):

   • Purpose: Retrieves an array of all entries (both files and directories) within the specified path.
   • Advantage: Unlike Dir.entries, Dir.children excludes the special entries . and .., reducing the need for additional filtering.

2. .select { |entry| File.directory?(File.join(path, entry)) }:

   • Purpose: Filters the array to include only directories.
   • How It Works:
     • File.join(path, entry): Combines the base path with each entry to form the full path of the entry.
     • File.directory?(full_path): Checks if the combined path points to a directory.
     • select: Iterates through each entry and selects those for which the block returns true (i.e., directories).

Example Usage:

path = "/path/to/your/directory"
directories = Dir.children(path).select { |entry| File.directory?(File.join(path, entry)) }
puts directories

Output:

subdirectory1
subdirectory2
subdirectory3

This script will list all subdirectories within the specified path, excluding any files.

Alternative One-Liner Using Dir.glob:

Another approach involves using Dir.glob with a directory pattern. This method is also concise but may be slightly less efficient compared to Dir.children with select.

directories = Dir.glob("#{path}/*/").map { |dir| File.basename(dir.chomp('/')) }

Explanation:

1. Dir.glob("#{path}/*/"):

   • Purpose: Matches all directories within the specified path by looking for entries that end with a /.
   • Output: Returns an array of directory paths with trailing slashes.

2. .map { |dir| File.basename(dir.chomp('/')) }:

   • Purpose: Strips the trailing slash and extracts just the directory name.
   • File.basename(dir.chomp('/')): Removes the trailing slash and retrieves the base name of the directory.

Example Usage:

path = "/path/to/your/directory"
directories = Dir.glob("#{path}/*/").map { |dir| File.basename(dir.chomp('/')) }
puts directories

Output:

subdirectory1
subdirectory2
subdirectory3

Choosing Between the Two Methods:

• Performance: Dir.children combined with select is generally more efficient because it avoids the need to process and map each path.
• Simplicity: Both methods are straightforward, but Dir.children is more readable when you need only directory names without additional processing.

Handling Full Paths:

If you require the full paths of the directories instead of just their names, you can modify the one-liner accordingly:

directories = Dir.children(path).select { |entry| File.directory?(File.join(path, entry)) }.map { |entry| File.join(path, entry) }

Example Usage:

path = "/path/to/your/directory"
directories = Dir.children(path).select { |entry| File.directory?(File.join(path, entry)) }.map { |entry| File.join(path, entry) }
puts directories

Output:

/path/to/your/directory/subdirectory1
/path/to/your/directory/subdirectory2
/path/to/your/directory/subdirectory3

Conclusion:

For the fastest and most optimized one-liner to retrieve an array of directories (excluding files) in Ruby, using Dir.children with select is highly recommended. It is both efficient and easy to understand, making it suitable for various applications where directory listings are required.

directories = Dir.children(path).select { |entry| File.directory?(File.join(path, entry)) }

This approach ensures you get a clean list of directories without unnecessary entries, leveraging Ruby's built-in methods for optimal performance.

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Happy coding!