问题
Am I missing something in the Array documentation? I have an array which contains up to one object satisfying a certain criterion. I'd like to efficiently find that object. The best idea I have from the docs is this:
candidates = my_array.select { |e| e.satisfies_condition? }
found_it = candidates.first if !candidates.empty?
But I am unsatisfied for two reasons:
- That
selectmade me traverse the whole array, even though we could have bailed after the first hit. - I needed a line of code (with a condition) to flatten the candidates.
Both operations are wasteful with foreknowledge that there's 0 or 1 satisfying objects.
What I'd like is something like:
array.find_first(block)
which returns nil or the first object for which the block evaluates to true, ending the traversal at that object.
Must I write this myself? All those other great methods in Array make me think it's there and I'm just not seeing it.
回答1:
Either I don't understand your question, or Enumerable#find is the thing you were looking for.
回答2:
use array detect method if you wanted to return first value where block returns true
[1,2,3,11,34].detect(&:even?) #=> 2
OR
[1,2,3,11,34].detect{|i| i.even?} #=> 2
If you wanted to return all values where block returns true then use select
[1,2,3,11,34].select(&:even?) #=> [2, 34]
回答3:
Guess you just missed the find method in the docs:
my_array.find {|e| e.satisfies_condition? }
回答4:
Do you need the object itself or do you just need to know if there is an object that satisfies. If the former then yes: use find:
found_object = my_array.find { |e| e.satisfies_condition? }
otherwise you can use any?
found_it = my_array.any? { |e| e.satisfies_condition? }
The latter will bail with "true" when it finds one that satisfies the condition. The former will do the same, but return the object.
来源：https://stackoverflow.com/questions/2381163/ruby-array-find-first-object