component array, the value is the group number
Given a self-relational array of arrays, for example, vertices_vertices, edges_edges, faces_faces, where the values in the inner arrays relate to the indices of the outer array, create collection groups where each item is included in a group if it points to another member in that group. The result will be in the form of an array matching in length the number of components, for each component, the value is its group number.
an array of arrays of numbers