So, from SRP, standpoint, too much happening here. How about:

```ruby
# YARD Docs
attr_reader :data

# YARD Docs
attr_reader :data_type

# @param ... add YARD docs
def initialize(alps_data, data_type = nil)
  @data = alps_data
  @data_type = data_type || alps_data_type(alps_data)
end

def to_hash
  @hash ||=  send("alps_#{data_type}_to_hash", data)
end

def alps_data_type(alps_data)
  if alps_data.is_a?(File)
    # Guess based on file name first
    if alps_data.path.ends_with?('json')
      :json
    elsif alps_data.path.ends_with?('xml')
      :xml
    else
       # Guess based on content second
       alps_data.read(1000).strip.first == '{' ? :json : :xml).tap { |_| alps_data.rewind }
    end
  else
      # Plain string - take content
      alps_data.strip.first == '{' ? :json : :xml
   end
end
```

Also, would make various methods private. Only thing public should be readers and #to_hash