Finding nearest objects

[SHC]

I’ve shared my tutorial “Using Grids For Collisions” on Google+ and there I’ve got a comment.

I use a different, very fast algorithm: First, sort all objects by their x-coordinate. Then calculate abs(x(n)-x(n-1)) to filter out those objects, which are nearby each other on x (can be done during sort), and only those you have to insert into a list, sort again by their y-coordinate. And if those left are also nearby on y, you have sorted out then all candidates for a more intense collision detection. The advantage is, if you use a sort algorithm, which likes pre-sorted data, its incredibly fast. Works for several hundred thousands of object coordinates (means polygons) in near real-time. No need to differentiate between unmovable and moving objects! And - because of the simplicity of the algorithm, it is typically translated into very fast machine code, avoiding cache - misses. And if you need to detect z-axis collisions, just add one more sorter. Works perfectly in fully dynamic worlds, where all objects move. Have fun!

I wanna try it but I don’t understand it. Can anybody help me understanding it so that I can implement?