Deeply extract all used symbols from a hash of nested symbols in an array

Question

I have a nested hash of symbols like this:

{
  a: {
    b: :c,
    d: {
      e: :f
    }
  },
  g: :h
}

I want to build an array that contains all symbols used in the hash, both keys and values, in any order. For the example above:

[:a, :b, :c, :d, :e, :f, :g, :h]

Is there any simple, fast and ruby-friendly way to do this?

I'm doing this with a recursive function that sums hash.keys with hash.values, and finally applies flatten to the result.

def all_keys(hash)
  hash.keys + hash.values.map { |e| e.is_a?(Hash) ? all_keys(e) : e }
end

Answer 1

Some notes:

• The flattening should be performed where the non-desired nesting is being introduced, not later. Use flat_map instead of map:

• Why e for the value name instead of v?

I'd write:

def all_keys(hash)
  hash.keys + hash.values.flat_map { |v| v.is_a?(Hash) ? all_keys(v) : [v] }
end

Another way to do it, slightly shorter, is to iterate directly the pairs. Pick the one which is more declarative to you:

def all_keys(hash)
  hash.flat_map { |k, v| [k] + (v.is_a?(Hash) ? all_keys(v) : [v]) }
end

Answer 2

A simple method would be to convert the Hash to an Array (recursively), flatten the Array to 1 level, and use Array#select to get just the symbols like

def all_symbols(h)
  h.map do |k,v|
    [k,v.is_a?(Hash) ? all_symbols(v) : v]
  end.flatten.select{|v| v.is_a?(Symbol)}
end 

my_hash = {a: {b: :c,d: {e: :f,"p"=>{"x" => :j}}},g: :h, "r" => "n"}
all_symbols(my_hash)
#=> [:a, :b, :c, :d, :e, :f, :j, :g, :h]