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

Question

To add a new pair to Hash I do:

{:a => 1, :b => 2}.merge!({:c => 3})   #=> {:a => 1, :b => 2, :c => 3} 

Is there a similar way to delete a key from Hash ?

This works:

{:a => 1, :b => 2}.reject! { |k| k == :a }   #=> {:b => 2} 

but I would expect to have something like:

{:a => 1, :b => 2}.delete!(:a)   #=> {:b => 2} 

It is important that the returning value will be the remaining hash, so I could do things like:

foo(my_hash.reject! { |k| k == my_key }) 

in one line.

Answer 1

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