Q:

How to replace all nil value with "" in a ruby hash recursively?

str = "<a><b><c></c></b></a>"
hash = Hash.from_xml(str)
# => {"a"=>{"b"=>{"c"=>nil}}}

How can I replace all nils in a Hash to "" so that the hash becomes:
{"a"=>{"b"=>{"c"=>""}}}

A:

Here is a recursive method that does not change the original hash.
Code
def denilize(h)
  h.each_with_object({}) { |(k,v),g|
    g[k] = (Hash === v) ?  denilize(v) : v.nil? ? '' : v }
end

Examples
h = { "a"=>{ "b"=>{ "c"=>nil } } }
denilize(h) #=> { "a"=>{ "b"=>{ "c"=>"" } } }

h = { "a"=>{ "b"=>{ "c"=>nil , "d"=>3, "e"=>nil}, "f"=>nil  } }
denilize(h) #=> { "a"=>{ "b"=>{ "c"=>"" , "d"=>3, "e"=>""}, "f"=>"" } } 

