Not quite sure what this is supposed to do. @ary is empty. So, you are undefining nothing at all. But, even if there was something to undefine, all it undefines is values, while the rest of the code uses keys. Hence, it seems to be pointless in stereo.

No it' not pointless in stereo. undef undefes values, correct. But undef *defines* the *keys* of the values.

       all
  it undefines is values

For a moment you had it there, to bad you didn't read your post.