Hash Remove All Except Specific Keys

Hash remove all except specific keys

Some other options:

h.select {|k,v| ["age", "address"].include?(k) }

Or you could do this:

class Hash
  def select_keys(*args)
    select {|k,v| args.include?(k) }
  end
end

So you can now just say:

h.select_keys("age", "address")

How to remove a key from Hash and get the remaining hash in Ruby/Rails?

Rails has an except/except! method that returns the hash with those keys removed. If you're already using Rails, there's no sense in creating your own version of this.

class Hash
  # Returns a hash that includes everything but the given keys.
  #   hash = { a: true, b: false, c: nil}
  #   hash.except(:c) # => { a: true, b: false}
  #   hash # => { a: true, b: false, c: nil}
  #
  # This is useful for limiting a set of parameters to everything but a few known toggles:
  #   @person.update(params[:person].except(:admin))
  def except(*keys)
    dup.except!(*keys)
  end

  # Replaces the hash without the given keys.
  #   hash = { a: true, b: false, c: nil}
  #   hash.except!(:c) # => { a: true, b: false}
  #   hash # => { a: true, b: false }
  def except!(*keys)
    keys.each { |key| delete(key) }
    self
  end
end

Remove a Hash key using except

You will have to use this to get the my_hash['user_attrbiutes'] except person_attributes:

2.1.0 :010 > my_hash['user_attributes'].except('person_attributes')
 => {"email"=>"email@email.com"} 

To get the output as {"user_attributes"=>{"email"=>"email@email.com"}} you can use:

 => {"user_attributes"=>{"email"=>"email@email.com", "person_attributes"=>{"first_name"=>"a_name", "last_name"=>"a_name"}}} 
2.1.0 :026 > my_hash['user_attributes'].delete('person_attributes')
 => {"first_name"=>"a_name", "last_name"=>"a_name"} 
2.1.0 :027 > my_hash
 => {"user_attributes"=>{"email"=>"email@email.com"}} 

remove specific keys (and values) from a ruby hash

Hash#except, Hash#except! do not accepts an array of keys, but keys as arbitrary parameters. You need to use * operator to convert the array into method arguments:

result_hash.except(*suppression_list)

Is there an elegant way to remove a specific key from a hash and it's sub-hashes in Ruby

I don't think there is a built in method for this so a simple recursive method along the following lines is one solution:

def recursive_delete(hash, to_remove)
  hash.delete(to_remove)
  hash.each_value do |value|
    recursive_delete(value, to_remove) if value.is_a? Hash
  end
end

With your example data:

h = { :action => "index", :controller => "home", :secret => "I love Jeff Atwood",
          :user => {:name => "Steve", :secret => "I steal Joel's pants"}}

recursive_delete(h, :secret)

puts h.inspect

Gives:

{:controller=>"home", :user=>{:name=>"Steve"}, :action=>"index"}

Note that this solution works in place i.e. it is modifying the original Hash, not returning a new Hash with the requested key excluded.

Delete all similar keys from nested hash

You can write a function to recursively traverse Hashes and Arrays.

def delete_recursively(thing, key_to_delete)
  case thing
  when Hash
    # Delete the key
    thing.delete(key_to_delete)

    # Recurse into each remaining hash value.
    thing.each_value do |value|
      delete_recursively(value, key_to_delete)
    end
  when Array
    # Recurse into each value of the array.
    thing.each do |value|
      delete_recursively(value, key_to_delete)
    end
  end
end

This can be expanded to include other data types as necessary.

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