Yes, you have to write your_sorting_routine or retrieve_key yourself. In Perl, there is no "neighbouring" hash key - hash keys have no defined order, as has been already pointed out.
لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

In reply to Re^3: compare previous and present hash key values by choroba
in thread compare previous and present hash key values by undisputed

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