Ruby regex key search

Question

http://ruby-doc.org/core-1.9.3/Hash.html#method-i-include-3F

It is possible to convert hash.has_key?(String) to have a regex search capabilities?

Solution 1

I would advise extending Hash with a new method instead of replacing has_key?.

class Hash
  def has_rkey?(search)
    search = Regexp.new(search.to_s) unless search.is_a?(Regexp)
    !!keys.detect{ |key| key =~ search }
  end
end

This will work with strings, symbols or a regexp as arguments.

irb> h = {:test => 1}
 => {:test=>1}  
irb> h.has_rkey?(:te)
 => true 
irb> h.has_rkey?("te")
 => true 
irb> h.has_rkey?(/te/)
 => true 
irb> h.has_rkey?("foo")
 => false 
irb> h.has_rkey?(:foo)
 => false 
irb> h.has_rkey?(/foo/)
 => false 

Solution 2

I think that using any? is a good solution as stated by qqbenq, but I would prefer using it with grep since it's more succinct.

hash.keys.grep(/regexp/).any?

Solution 3

If you are only interested in a yes/no answer, then any? might be a good option:

hash.keys.any? { |key| key.to_s.match(regexp)}

where regexp is a regular expression.

Solution 4

I am not aware of an absolute answer for this question but if I were to write a hacky method for this, I would do this

!!hash.keys.detect{ |k| k.to_s =~ /Your_Regex_here/ }

This will return true when any key matches regex and false otherwise.

View more solutions

Comments

[Kyle]

just a tip, detect will stop as soon as it finds an element where the predicate returns true. This would prevent you from having to iterate over the entire collection and then checking and array with empty?

[the911s]

Be advised that this changes the lookup time complexity of the hash data structure from O(1) to O(n)... which depending on your intended usage may completely obviate the benefit of using a hash.

[the911s]

Follow-up thought: If you have to do this for a large set of data, you should consider building some type of index. For instance, in some databases, you could create an index on a regex dba.stackexchange.com/questions/10694/…

[Mark Thomas]

any is superior to detect, as it returns a boolean as desired. Note you have a typo: key => keys

[qqbenq]

Thanks, the typo is fixed, and yes, the main reason of this - late - answer was to provide a way where you don't have to !! to get a boolean.

[Tim K.]

hash.keys.find {...} will return the key name, if needed