How do I convert a Ruby hash so that all of its keys are symbols?

Question

I have a Ruby hash which looks like:

{ \"id\" => \"123\", \"name\" => \"test\" }

I would like to convert it to:

{ :id         


        

Answer 1

hash = {"apple" => "banana", "coconut" => "domino"}
Hash[hash.map{ |k, v| [k.to_sym, v] }]
#=> {:apple=>"banana", :coconut=>"domino"}

@mu is too short: Didn't see word "recursive", but if you insist (along with protection against non-existent to_sym, just want to remind that in Ruby 1.8 1.to_sym == nil, so playing with some key types can be misleading):

hash = {"a" => {"b" => "c"}, "d" => "e", Object.new => "g"}

s2s = 
  lambda do |h| 
    Hash === h ? 
      Hash[
        h.map do |k, v| 
          [k.respond_to?(:to_sym) ? k.to_sym : k, s2s[v]] 
        end 
      ] : h 
  end

s2s[hash] #=> {:d=>"e", #<Object:0x100396ee8>=>"g", :a=>{:b=>"c"}}

Answer 2

If you happen to be in Rails then you'll have symbolize_keys:

Return a new hash with all keys converted to symbols, as long as they respond to to_sym.

and symbolize_keys! which does the same but operates in-place. So, if you're in Rails, you could:

hash.symbolize_keys!

If you want to recursively symbolize inner hashes then I think you'd have to do it yourself but with something like this:

def symbolize_keys_deep!(h)
  h.keys.each do |k|
    ks    = k.to_sym
    h[ks] = h.delete k
    symbolize_keys_deep! h[ks] if h[ks].kind_of? Hash
  end
end

You might want to play with the kind_of? Hash to match your specific circumstances; using respond_to? :keys might make more sense. And if you want to allow for keys that don't understand to_sym, then:

def symbolize_keys_deep!(h)
  h.keys.each do |k|
    ks    = k.respond_to?(:to_sym) ? k.to_sym : k
    h[ks] = h.delete k # Preserve order even when k == ks
    symbolize_keys_deep! h[ks] if h[ks].kind_of? Hash
  end
end

Note that h[ks] = h.delete k doesn't change the content of the Hash when k == ks but it will preserve the order when you're using Ruby 1.9+. You could also use the [(key.to_sym rescue key) || key] approach that Rails uses in their symbolize_keys! but I think that's an abuse of the exception handling system.

The second symbolize_keys_deep! turns this:

{ 'a' => 'b', 'c' => { 'd' => { 'e' => 'f' }, 'g' => 'h' }, ['i'] => 'j' }

into this:

{ :a => 'b', :c => { :d => { :e => 'f' }, :g => 'h' }, ['i'] => 'j' }

You could monkey patch either version of symbolize_keys_deep! into Hash if you really wanted to but I generally stay away from monkey patching unless I have very good reasons to do it.

Answer 3

Just in case you are parsing JSON, from the JSON docs you can add the option to symbolize the keys upon parsing:

hash = JSON.parse(json_data, symbolize_names: true)

Answer 4

You can also extend core Hash ruby class placing a /lib/hash.rb file :

class Hash
  def symbolize_keys_deep!
    new_hash = {}
    keys.each do |k|
      ks    = k.respond_to?(:to_sym) ? k.to_sym : k
      if values_at(k).first.kind_of? Hash or values_at(k).first.kind_of? Array
        new_hash[ks] = values_at(k).first.send(:symbolize_keys_deep!)
      else
        new_hash[ks] = values_at(k).first
      end
    end

    new_hash
  end
end

If you want to make sure keys of any hash wrapped into arrays inside your parent hash are symbolized, you need to extend also array class creating a "array.rb" file with that code :

class Array
  def symbolize_keys_deep!
    new_ar = []
    self.each do |value|
      new_value = value
      if value.is_a? Hash or value.is_a? Array
        new_value = value.symbolize_keys_deep!
      end
      new_ar << new_value
    end
    new_ar
  end
end

This allows to call "symbolize_keys_deep!" on any hash variable like this :

myhash.symbolize_keys_deep!

Answer 5

I'm partial to:

irb
ruby-1.9.2-p290 :001 > hash = {"apple" => "banana", "coconut" => "domino"}
{
      "apple" => "banana",
    "coconut" => "domino"
}
ruby-1.9.2-p290 :002 > hash.inject({}){ |h, (n,v)| h[n.to_sym] = v; h }
{
      :apple => "banana",
    :coconut => "domino"
}

This works because we're iterating over the hash and building a new one on the fly. It isn't recursive, but you could figure that out from looking at some of the other answers.

hash.inject({}){ |h, (n,v)| h[n.to_sym] = v; h }

Answer 6

def symbolize_keys(hash)
   new={}
   hash.map do |key,value|
        if value.is_a?(Hash)
          value = symbolize_keys(value) 
        end
        new[key.to_sym]=value
   end        
   return new

end  
puts symbolize_keys("c"=>{"a"=>2,"k"=>{"e"=>9}})
#{:c=>{:a=>2, :k=>{:e=>9}}}