1

Using .flatten is a handy little trick to take an array of sub-arrays and turn it into a single array. For example: [[1,3],2,[5,8]].flatten => [1,3,2,5,8] You can even include nil [1,[2,nil],3].flatten will result in [1,2,nil,3].

This kind of method is very useful when nesting a .map method, but how would you account for an empty sub-array? For example: [1,[2,3],[],4].flatten would return [1,2,3,4]... but what if I need to keep track of the empty sub array maybe turn the result into [1,2,3,0,4] or [1,2,3,nil,4]

Is there any elegant way to do this? Or would I need to write some method to iterate through each individual sub-array and check it one by one?

Improve this question
1
  • Do you need to check for nested empty arrays, ie [1, [2, 3, []], 4]? Commented Feb 21, 2017 at 19:57

2 Answers 2

Reset to default
5

If you don't need to recursively check nested sub-arrays:

[1,[2,3],[],4].map { |a| a == [] ? nil : a }.flatten
Improve this answer
Sign up to request clarification or add additional context in comments.

3 Comments

This is a bit cleaner than what i had. I changed a == [] to a.any? but similar concept... For some reason I always overlook putting logic into my .map blocks.
@jkessluk won't a.any? choke on items which aren't arrays?
Yes, but I'm using this in a helper method where I've already ensured that the item passed through is an array. Otherwise, yes. You're correct.
2

First map the empty arrays into nils, then flatten

[1,2,[1,2,3],[]].map{|x| if x.is_a? Array and x.empty? then nil else x end}.flatten
Improve this answer

Comments

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.