Newbea question again?

Hello RoR Developers,

I have tiny problem about comparison. I have a array and hash. I want to
compare array elements with hash keys.
more details:
this is my hash, I create it from yaml file
my yaml file
template_of_roster3: template_of_roster2
template_of_roster4: template_of_roster3

@get_config == Hash

and my array

my question here is that how can I compare array with hash keys and how
can I can send warning message to user?
warn “warning message”

something like this.