Sorting by nested selector

[Barry]

I'm trying to sort an array of found locations by the count reviews that have said location filled in in the page field.

I have the following:

$locations = $pages->find("template=location, location_images!='', sort=count[template=review, location=$should_name_of_location_with_images]");

I know the nested selector isn't right. But what I'm trying to illustrate what i'm trying to achieve, which is to find locations which have at least 1 image and sort them by the count of pages with template "review" and have the location that has at least 1 image filled in in the location page field set in review.