Removing all empty elements from a hash / YAML?

Question

Rails 4.1 added Hash#compact and Hash#compact! as a core extensions to Ruby's Hash class. You can use them like this:

hash = { a: true, b: false, c: nil }
hash.compact                        
# => { a: true, b: false }
hash                                
# => { a: true, b: false, c: nil }
hash.compact!                        
# => { a: true, b: false }
hash                                
# => { a: true, b: false }
{ c: nil }.compact                  
# => {}

Heads up: this implementation is not recursive. As a curiosity, they implemented it using #select instead of #delete_if for performance reasons. See here for the benchmark.

In case you want to backport it to your Rails 3 app:

# config/initializers/rails4_backports.rb

class Hash
  # as implemented in Rails 4
  # File activesupport/lib/active_support/core_ext/hash/compact.rb, line 8
  def compact
    self.select { |_, value| !value.nil? }
  end
end

Use hsh.delete_if. In your specific case, something like: hsh.delete_if { |k, v| v.empty? }

You could add a compact method to Hash like this

class Hash
  def compact
    delete_if { |k, v| v.nil? }
  end
end

or for a version that supports recursion

class Hash
  def compact(opts={})
    inject({}) do |new_hash, (k,v)|
      if !v.nil?
        new_hash[k] = opts[:recurse] && v.class == Hash ? v.compact(opts) : v
      end
      new_hash
    end
  end
end

compact_blank (Rails 6.1+)

If you are using Rails (or a standalone ActiveSupport), starting from version 6.1, there is a compact_blank method which removes blank values from hashes.

It uses Object#blank? under the hood for determining if an item is blank.

{ a: "", b: 1, c: nil, d: [], e: false, f: true }.compact_blank
# => { b: 1, f: true }

Here is a link to the docs and a link to the relative PR.

A destructive variant is also available. See Hash#compact_blank!.

---

If you need to remove only nil values,

please, consider using Ruby build-in Hash#compact and Hash#compact! methods.

{ a: 1, b: false, c: nil }.compact
# => { a: 1, b: false }

If you're using Ruby 2.4+, you can call compact and compact!

h = { a: 1, b: false, c: nil }
h.compact! #=> { a: 1, b: false }

https://ruby-doc.org/core-2.4.0/Hash.html#method-i-compact-21

This one would delete empty hashes too:

swoop = Proc.new { |k, v| v.delete_if(&swoop) if v.kind_of?(Hash);  v.empty? }
hsh.delete_if &swoop