Filter a ruby array based on values in another array

Question

I have an array of extensions and an array of file names:

exts = ['.zip', '.tgz', '.sql']
files = ['file1.txt', 'file2.doc', 'file2.tgz', 'file3.sql', 'file6.foo', 'file4.zip']

I want to filter the file names by one or more matching extensions. In this case, the result would be:

["file1.zip", "file2.tgz", "file3.sql", "file4.zip"]

I know I can do this with a nested loop:

exts.each_with_object([]) do |ext, arr|
    files.each do |file| 
        arr << entry if file.include?(ext)
    end
end

This feels ugly to me. With select, I can avoid the feeling of nested loops:

files.select { |file| exts.each { |ext| file.include?(ext) } }

This works and feels better. Is there still a more elegant way that I'm missing?

Where do the entries in files come from? If you are filtering files in a directory, Dir.glob could be a better approach. — Stefan
– Stefan, Commented Nov 11, 2022 at 10:15
Thanks, they do come from a glob, and that’s the approach I use – this is just an example. — Steve K
– Steve K, Commented Nov 11, 2022 at 12:41
FWIW, it’s a helpful reminder that a matching via a glob would probably be a better approach for this specific case. I probably could have used a more generic example to suit the question. — Steve K
– Steve K, Commented Nov 11, 2022 at 13:08

spickermann · Accepted Answer · 2022-11-11 05:38:54Z

2

I would use Enumerable#grep with a regexp like this:

exts = ['.zip', '.tgz', '.sql']
files = ['file1.txt', 'file2.doc', 'file2.tgz', 'file3.sql', 'file6.foo', 'file4.zip']

files.grep(/#{Regexp.union(exts)}$/)
#=> ["file2.tgz", "file3.sql", "file4.zip"]

I use Regexp.union instead of a simple exts.join('|') because exts include dots (.) which have a special meaning in regular expressions. Regexp.union escapes those dots automatically.

edited Nov 11, 2022 at 5:38

answered Nov 11, 2022 at 5:30

spickermann

108k9 gold badges115 silver badges147 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Steve K Over a year ago

Thanks! It’s funny you mention this – I had added grep as a potential path I could take, but I missed the regex piece here. I think this is really clean.

Steve K · Accepted Answer · 2022-11-11 13:10:55Z

0

Thinking about it a bit further, I realized I could make the select better if I changed the logic slightly:

exts = ['zip', 'tgz', 'sql']
files.select{ |file| exts.include?(file) }

As far as I can tell, this is as clean as I can get.

edited Nov 11, 2022 at 13:10

answered Nov 11, 2022 at 2:52

Steve K

3871 gold badge8 silver badges25 bronze badges

2 Comments

Cary Swoveland Over a year ago

I think it would be more clear if you wrote exts = ['zip', 'tgz', 'sql']. Then files.select { |f| exts.any? { |ext| f.end_with?(ext) } } or files.select { |f| exts.any? { |ext| File.extname(f) == ext } }.

Steve K Over a year ago

Thanks, I did mean files. I agree that adding the extensions array to this example would make it more clear. any? I knew, but end_with? was new to me; thanks for that. This suggestion is very readable. I think you ought to add this as a possibility answer.

Sergio Tulentsev · Accepted Answer · 2022-11-11 13:14:30Z

0

If you store extensions in a set, you'll reduce the runtime complexity from O(NM) to O(N).

exts = ['.zip', '.tgz', '.sql'].to_set
files.select { |file| exts.include?(File.extname(file)) }

answered Nov 11, 2022 at 13:14

Sergio Tulentsev

231k43 gold badges381 silver badges373 bronze badges

Collectives™ on Stack Overflow

Filter a ruby array based on values in another array

3 Answers 3

1 Comment

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related