How do I spawn 30 objects on grid of 60 spaces

Hi all, please help.

I am wanting to spawn 30 items at random positions on a grid. I have set up 60 spawn points and I would like to spawn 30 items at any 30 random points but so that they don't overlay each other.

This is the grid

The red dot has to spawn once on a separate yellow spawn point , 30 times.

What's the best way to achieve this.

Thanks

RandomArray2 is very helpful.

plugin-randomarray_t63557?start=10 (look at last post - points to https://github.com/nutmix/RandomArray2)