Parametric design in MoI?

 From:  wastzzz
7713.474 
I have 3 different objects: a, b, c.
How do I linear array them randomly? For instance a,a,b,a,c,c,a,b,b,a etc..
My main purpose using nodeeditor is random management of objects, but I can't seem to understand.. I cannot find a "linear array" node, only circular.

Thanks.
M.