Check if key exists in hash

In Ruby on Rails Programming you might have to check if key exists in hash and based on that you might have to perform other operation. There is a simple way to detect if key exists in particular hash.

Ruby Hashes

Ruby hash contains Key-Value pairs. In Ruby, you can create a simple hash as follows,

my_hash = {}

Above code will initialize empty hash. Let’s add some key value pair in the my_hash

my_hash['name'] = 'Ruby in Rails'

The above code will add ‘name’ key and ‘Ruby in Rails’ as it’s value. Let’s add one more key-value pair in the my_hash

my_hash['type'] = 'Ruby Programming Tutorials'


How to check if key exists in hash

You can check if particular key exists in a hash or not by using has_key? method available for the hash object in ruby.

Syntax Description
hash#has_key? sample This will return true/false by
checking if key sample exists in
hash object for which the method is invoked
my_hash.has_key? 'name'
=> true

This will return true as name key exists in the my_hash hash

my_hash.has_key? 'abc'
=> false

Above code returns false as my_hash doesn’t contain any key with named abc

Performance of Hash#has_key? versun Array#include?
Parameter Hash#has_key? Array#include
Time Complexity o(1) operation o(n) operation
Access Type Accesses Hash[key] if
it returns any value
then true is returned
to the Hash#has_key? call
Iterates through each
element of the array till it
finds the value in Array


You can find more about ruby hashes and various methods that can be used with hashes on apidock. We learned how to check if key exists in a hash for Ruby language and compared it with include operation on arrays.

The has_key is faster as it is o(1) lookup as explained above.