def chunk_suffixes
      chunks.map { |chunk| File.extname(chunk).split("-").last }.sort
    end
def chunk_suffixes
      chunks.map { |chunk| File.extname(chunk).split("-").last }.sort
    end
Returns an array of suffixes for each chunk, in alphabetical order.
 For example: [aa, ab, ac, ad, ae] or [aaa, aab, aac aad]