ŒĠ - Group Multidimensional Indices by Value
Tags: miscellaneous , array , number
This atom is monadic, which means it takes one argument.
Group the multidimensional indices of a list by the corresponding values.
This returns a list of lists. Each multidimensional index of
z will appear exactly once. Two indices are in the same sublist if and only if their corresponding values are equal. The sublists are ordered by the element they correspond to.