In Ruby >= 2.5 (docs) you can use:
my_hash.transform_keys(&:to_sym)
Using older Ruby version? Here is a one-liner that will copy the hash into a new one with the keys symbolized:
my_hash = my_hash.inject({}){|memo,(k,v)| memo[k.to_sym] = v; memo}
With Rails you can use:
my_hash.symbolize_keys
my_hash.deep_symbolize_keys
Here's a better method, if you're using Rails:
params.symbolize_keys
The end.
If you're not, just rip off their code (it's also in the link):
myhash.keys.each do |key|
myhash[(key.to_sym rescue key) || key] = myhash.delete(key)
end
For the specific case of YAML in Ruby, if the keys begin with ':', they will be automatically interned as symbols.
require 'yaml'
require 'pp'
yaml_str = "
connections:
- host: host1.example.com
port: 10000
- host: host2.example.com
port: 20000
"
yaml_sym = "
:connections:
- :host: host1.example.com
:port: 10000
- :host: host2.example.com
:port: 20000
"
pp yaml_str = YAML.load(yaml_str)
puts yaml_str.keys.first.class
pp yaml_sym = YAML.load(yaml_sym)
puts yaml_sym.keys.first.class
Output:
# /opt/ruby-1.8.6-p287/bin/ruby ~/test.rb
{"connections"=>
[{"port"=>10000, "host"=>"host1.example.com"},
{"port"=>20000, "host"=>"host2.example.com"}]}
String
{:connections=>
[{:port=>10000, :host=>"host1.example.com"},
{:port=>20000, :host=>"host2.example.com"}]}
Symbol
if you're using Rails, it is much simpler - you can use a HashWithIndifferentAccess and access the keys both as String and as Symbols:
my_hash.with_indifferent_access
see also:
http://api.rubyonrails.org/classes/ActiveSupport/HashWithIndifferentAccess.html
Or you can use the awesome "Facets of Ruby" Gem, which contains a lot of extensions to Ruby Core and Standard Library classes.
require 'facets'
> {'some' => 'thing', 'foo' => 'bar'}.symbolize_keys
=> {:some=>"thing", :foo=>"bar}
Since Ruby 2.5.0 you can use Hash#transform_keys or Hash#transform_keys!.
{'a' => 1, 'b' => 2}.transform_keys(&:to_sym) #=> {:a => 1, :b => 2}
http://api.rubyonrails.org/classes/Hash.html#method-i-symbolize_keys
hash = { 'name' => 'Rob', 'age' => '28' }
hash.symbolize_keys
# => { name: "Rob", age: "28" }
You could be lazy, and wrap it in a lambda:
my_hash = YAML.load_file('yml')
my_lamb = lambda { |key| my_hash[key.to_s] }
my_lamb[:a] == my_hash['a'] #=> true
But this would only work for reading from the hash - not writing.
To do that, you could use Hash#merge
my_hash = Hash.new { |h,k| h[k] = h[k.to_s] }.merge(YAML.load_file('yml'))
The init block will convert the keys one time on demand, though if you update the value for the string version of the key after accessing the symbol version, the symbol version won't be updated.
irb> x = { 'a' => 1, 'b' => 2 }
#=> {"a"=>1, "b"=>2}
irb> y = Hash.new { |h,k| h[k] = h[k.to_s] }.merge(x)
#=> {"a"=>1, "b"=>2}
irb> y[:a] # the key :a doesn't exist for y, so the init block is called
#=> 1
irb> y
#=> {"a"=>1, :a=>1, "b"=>2}
irb> y[:a] # the key :a now exists for y, so the init block is isn't called
#=> 1
irb> y['a'] = 3
#=> 3
irb> y
#=> {"a"=>3, :a=>1, "b"=>2}
You could also have the init block not update the hash, which would protect you from that kind of error, but you'd still be vulnerable to the opposite - updating the symbol version wouldn't update the string version:
irb> q = { 'c' => 4, 'd' => 5 }
#=> {"c"=>4, "d"=>5}
irb> r = Hash.new { |h,k| h[k.to_s] }.merge(q)
#=> {"c"=>4, "d"=>5}
irb> r[:c] # init block is called
#=> 4
irb> r
#=> {"c"=>4, "d"=>5}
irb> r[:c] # init block is called again, since this key still isn't in r
#=> 4
irb> r[:c] = 7
#=> 7
irb> r
#=> {:c=>7, "c"=>4, "d"=>5}
So the thing to be careful of with these is switching between the two key forms. Stick with one.
This is for people who uses mruby and do not have any symbolize_keys method defined:
class Hash
def symbolize_keys!
self.keys.each do |k|
if self[k].is_a? Hash
self[k].symbolize_keys!
end
if k.is_a? String
raise RuntimeError, "Symbolizing key '#{k}' means overwrite some data (key :#{k} exists)" if self[k.to_sym]
self[k.to_sym] = self[k]
self.delete(k)
end
end
return self
end
end
The method:
StringRuntimeErrorstrings = ["HTML", "CSS", "JavaScript", "Python", "Ruby"]
symbols = [ ]
strings.each {|x| symbols.push(x.intern)}
So this is probably the most straightforward way to convert strings to symbols in your array(s) in Ruby. Make an array of strings then make a new variable and set the variable to an empty array. Then select each element in the first array you created with the ".each" method. Then use a block code to ".push" all of the elements in your new array and use ".intern or .to_sym" to convert all the elements to symbols.
Symbols are faster because they save more memory within your code and you can only use them once. Symbols are most commonly used for keys in hash which is great. I'm the not the best ruby programmer but this form of code helped me a lot.If anyone knows a better way please share and you can use this method for hash too!
If you would like vanilla ruby solution and as me do not have access to ActiveSupport here is deep symbolize solution (very similar to previous ones)
def deep_convert(element)
return element.collect { |e| deep_convert(e) } if element.is_a?(Array)
return element.inject({}) { |sh,(k,v)| sh[k.to_sym] = deep_convert(v); sh } if element.is_a?(Hash)
element
end
Starting on Psych 3.0 you can add the symbolize_names: option
Psych.load("---\n foo: bar")
# => {"foo"=>"bar"}
Psych.load("---\n foo: bar", symbolize_names: true)
# => {:foo=>"bar"}
Note: if you have a lower Psych version than 3.0 symbolize_names: will be silently ignored.
My Ubuntu 18.04 includes it out of the box with ruby 2.5.1p57
This is not exactly a one-liner, but it turns all string keys into symbols, also the nested ones:
def recursive_symbolize_keys(my_hash)
case my_hash
when Hash
Hash[
my_hash.map do |key, value|
[ key.respond_to?(:to_sym) ? key.to_sym : key, recursive_symbolize_keys(value) ]
end
]
when Enumerable
my_hash.map { |value| recursive_symbolize_keys(value) }
else
my_hash
end
end
I like this one-liner, when I'm not using Rails, because then I don't have to make a second hash and hold two sets of data while I'm processing it:
my_hash = { "a" => 1, "b" => "string", "c" => true }
my_hash.keys.each { |key| my_hash[key.to_sym] = my_hash.delete(key) }
my_hash
=> {:a=>1, :b=>"string", :c=>true}
Hash#delete returns the value of the deleted key
Facets' Hash#deep_rekey is also a good option, especially:
Sample:
require 'facets/hash/deep_rekey'
my_hash = YAML.load_file('yml').deep_rekey
In ruby I find this to be the most simple and easy to understand way to turn string keys in hashes to symbols :
my_hash.keys.each { |key| my_hash[key.to_sym] = my_hash.delete(key)}
For each key in the hash we call delete on it which removes it from the hash (also delete returns the value associated with the key that was deleted) and we immediately set this equal to the symbolized key.
Similar to previous solutions but written a bit differently.
Code does not mutate the hash been passed in.
module HashUtils
def symbolize_keys(hash)
transformer_function = ->(key) { key.to_sym }
transform_keys(hash, transformer_function)
end
def stringify_keys(hash)
transformer_function = ->(key) { key.to_s }
transform_keys(hash, transformer_function)
end
def transform_keys(obj, transformer_function)
case obj
when Array
obj.map{|value| transform_keys(value, transformer_function)}
when Hash
obj.each_with_object({}) do |(key, value), hash|
hash[transformer_function.call(key)] = transform_keys(value, transformer_function)
end
else
obj
end
end
end
hash.symbolize_keysandhash.deep_symbolize_keysdo the job if you're using Rails. - Zaz