How to find a hash key containing a matching value

Question

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"})

You could use Enumerable#select:

clients.select{|key, hash| hash["client_id"] == "2180" }
#=> [["orange", {"client_id"=>"2180"}]]

Note that the result will be an array of all the matching values, where each is an array of the key and value.

You can invert the hash. clients.invert["client_id"=>"2180"] returns "orange"

You could use hashname.key(valuename)

Or, an inversion may be in order. new_hash = hashname.invert will give you a new_hash that lets you do things more traditionally.

try this:

clients.find{|key,value| value["client_id"] == "2178"}.first

According to ruby doc http://www.ruby-doc.org/core-1.9.3/Hash.html#method-i-key key(value) is the method to find the key on the base of value.

ROLE = {"customer" => 1, "designer" => 2, "admin" => 100}
ROLE.key(2)

it will return the "designer".