@Richard Well, using ⌸ was pretty obvious, since we need to count size of groups of elements that share a trait (negativeness, positiveness; i.e. the sign). Then we just need to sum them up and adjust the sign, which we can do using the sign too.
> Write a function that will reshape a given array into the smallest square matrix that will contain all the elements of the argument, padding with additional elements if necessary. The pad element should be 0 if the array is numeric and space ' ' if the array is character.
Little sidestep. Why not introduce a circle with a dot in it ⊙ for outer product? And of course keep the ∘. It is the only function which uses two characters. Probably stupid question as newcomer / non programmer