Retrieve entries by random sort, then resort alphabetically I need to pull X entries with

{% set randEntries = craft.entries.section('presenters').order('RAND()').limit(10) %}


But then sort them alphabetically on entry.lastName.

Do I need to Supersort for this, and if so, how do I apply it? Do I need to pull the entries first, and then run the sort?
I recon Supersort is they way to go, as its got some really handy functions to make this sort of thing a breeze. Try with the following:

{% set entries = craft.entries.section('presenters').order('RAND()').limit(10) %}
{% set sortedEntries = entries | supersort('sortAs', '{lastName}') %}

{% for item in sortedEntries %}
    {{ item.title }}
{% endfor %}