hash.md

Create hash

Create empty hash

hash = {}

Create hash with defined keys and values

hash = {
  key1: 'val1',
  key2: 'val2',
  key3: 'val3'
}

Get hash key value

hash = {
  key1: 'val1',
  key2: 'val2'
}

hash[:key1] # => 'val1'

If key is not defined in the hash, it will return nil value.

hash[:missing] # => nil

To return value even if the key is not defined, we can use method fetch with second parameter that defines what value should be returned.

hash.fetch(:missing, 'val') # => 'val'

Without the second parameter fetch method will raise exception if the key is missing.

hash.fetch(:missing) # => KeyError (key not found: :missing)

You can even pass block to the fetch method.

hash.fetch(:key) do
  # executed if key is missing
end

It is possible to retrieve values from multiple keys at once using values_at method.

hash.values_at(:key1, :key2) # => ['val1', 'val2']

Set hash value

hash[:key5] = 'val5'
hash[:key5] # => 'val5'

The keys of the hash do not have to be strings or symbols. Key of the hash can be any object.

hash['str'] = 'test'
hash[1000] = 'test'
hash[Object.new] = 'test'

Nested hashes

Value assigned to hash key can be another hash.

hash = {
  key1: 'val1'
  key2: {
    xyz: 'test'
  }
}

hash[:key2][:xyz] # => 'test'

Since ruby version 2.3 you can use method dig to get values from the nested hash.

hash.dig(:key2, :xyz) # => 'test'

Other functions

hash = {
  key1: 'val1',
  key2: 'val2'
}

Get hash keys

hash.keys # => [:key1, :key2]

Get hash values

hash.values # => ['val1', 'val2']

Hash size

hash.size # => 2
hash.length # => 2

Merge hashes

hash2 = { xyz: 'xyz' }
hash.merge(hash2) # => { key1: 'val1', key2: 'val2', xyz: 'xyz' }
hash # => { key1: 'val1', key2: 'key2' }

Method merge does not change the original hash. To change the original hash you have to use merge! method.

hash.merge!(hash2) # => { key1: 'val1', key2: 'val2', xyz: 'xyz' }
hash # => { key1: 'val1', key2: 'key2', xyz: 'xyz' }