Comments on: Selecting matching key/value pairs from a hash

By: Matthew Bass

Matthew Bass — Tue, 06 Mar 2007 15:57:09 +0000

Mike sends in another example for us, one that doesn't copy the entire hash using symbolize_keys first:

class Hash
 def select_all(*attrs)
   reject { |k, v| !attrs.include?(k.to_sym) }
 end
end

Matthew Bass — Tue, 06 Mar 2007 13:48:03 +0000

Pit e-mailed me directly with this alternate solution:

def select_all(*attrs)
  (keys & attrs).inject({}) { |h, k| h[k] = self[k] }
end

Not bad. He says that depending on the size of the hash and the number of attributes, this
implementation could be faster.

Austin Taylor — Tue, 06 Mar 2007 05:41:18 +0000

I would call it #select_keys, and I would glob lib/ in environment.rb.