How to get value of key or key presence from neste

问题:

How do I get the value of a key or the key's presence from a nested hash?

For example:

a = { "a"=> { "b" => 1, "c" => { "d" => 2, "e" => { "f" => 3 } }}, "g" => 4}

Is there any direct method to get the value of "f"? Or is there a method to know the presence of key in the nested hash?

回答1:

%w[a c e f].inject(a, &:fetch) # => 3
%w[a c e x].inject(a, &:fetch) # > Error key not found: "x"
%w[x].inject(a, &:fetch) # => Error key not found: "x"

Or, to avoid errors:

%w[a c e f].inject(a, &:fetch) rescue "Key not found" # => 3
%w[a c e x].inject(a, &:fetch) rescue "Key not found"  # => Key not found
%w[x].inject(a, &:fetch) rescue "Key not found"  # => Key not found

回答2:

def is_key_present?(hash, key)
  return true if hash.has_key?(key)
  hash.each do |k, v|
    return true if v.kind_of?(Hash) and is_key_present?(v, key)
  end
  false
end

> is_key_present?(a, 'f')
=> true