c_rs_table: Contingency table from membership vectors
Description
Given two membership vectors, returns the corresponding contingency table.
we assume the labels are >=1 and numbered consecutively. If not consecutive
(some labels are unused) this implementation still works, but will be less
efficient.
Usage
c_rs_table(c1, c2)
Arguments
c1, c2
membership vectors (integer values containing the index of each community)