Ruby: filter array by regex?

Question

This is a common, repetitive idiom for me: filtering an array using a regular expression, and returning a sub-array. My approach doesn't seem very Ruby-like (I come from Java). I end up having many methods which look a lot like this.

What is the idiomatic Ruby way to improve this code?

def get_all_gifs(items_)   output = Array.new   filter = /\.jpg$/   items_.each do |item|     next if item =~ filter     output << item   end   output end 

Answer 1

If you want to find all gifs:

def get_all_gifs(files)   files.select{ |i| i[/\.gif$/] } end 

If you want to find all jpegs:

def get_all_jpgs(files)   files.select{ |i| i[/\.jpe?g$/] } end 

Running them:

files = %w[foo.gif bar.jpg foo.jpeg bar.gif] get_all_gifs(files) # => ["foo.gif", "bar.gif"] get_all_jpgs(files) # => ["bar.jpg", "foo.jpeg"] 

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But wait! There's more!

What if you want to group them all by their type, then extract based on the extension?:

def get_all_images_by_type(files)   files.group_by{ |f| File.extname(f) } end 

Here's the types of files:

get_all_images_by_type(files).keys # => [".gif", ".jpg", ".jpeg"] 

Here's how to grab specific types:

get_all_images_by_type(files) # => {".gif"=>["foo.gif", "bar.gif"], ".jpg"=>["bar.jpg"], ".jpeg"=>["foo.jpeg"]} get_all_images_by_type(files)['.gif'] # => ["foo.gif", "bar.gif"] get_all_images_by_type(files).values_at('.jpg', '.jpeg') # => [["bar.jpg"], ["foo.jpeg"]] 

Answer 2

Have a look at Enumerable.grep, it's a very powerful way of finding/filtering things in anything enumerable.