I've always wished that Sort::Key provided such functions.

In case you're not familiar with Sort::Key, at its core is keysort KEY_GENERATOR LIST, which could be used as follows:

# Sort the objects according to the value of their `name` attribute.
my @sorted_objects =
   keysort { $_->name }
      @unsorted_objects;
[download]

It has variants.

# Sort the objects according to the value of their uint id
my @sorted_objects =
   ukeysort { $_->id }
      @unsorted_objects;
[download]

You'd think the module would also provide similar subs to find the elements that would sort first and/or last, but it doesn't.

Your argmin and argmax sub are effectively specific variants of those missing subs.