ruby - How to find a hash key containing a matching value

Question

Given I have the below clients hash, is there a quick ruby way (without having to write a multi-line script) to obtain the key given I want to match the client_id? E.g. How to get the key for client_id == "2180"?

clients = {
  "yellow"=>{"client_id"=>"2178"}, 
  "orange"=>{"client_id"=>"2180"}, 
  "red"=>{"client_id"=>"2179"}, 
  "blue"=>{"client_id"=>"2181"}
}

Answer 1

Ruby 1.9 and greater:

hash.key(value) => key

Ruby 1.8:

You could use hash.index

hsh.index(value) => key

Returns the key for a given value. If not found, returns nil.

h = { "a" => 100, "b" => 200 }
h.index(200) #=> "b"
h.index(999) #=> nil

So to get "orange", you could just use:

clients.key({"client_id" => "2180"})