[ruby-on-rails] TypeError: no implicit conversion of Symbol into Integer

You probably meant this:

require 'active_support/core_ext' # for titleize

myHash = {company_name:"MyCompany", street:"Mainstreet", postcode:"1234", city:"MyCity", free_seats:"3"}

def cleanup string
  string.titleize
end

def format(hash)
  output = {}
  output[:company_name] = cleanup(hash[:company_name])
  output[:street] = cleanup(hash[:street])
  output
end

format(myHash) # => {:company_name=>"My Company", :street=>"Mainstreet"}

Please read documentation on Hash#each