  We investigate degree correlations in two online social networks where users
are connected through different types of links. We find that, while subnetworks
in which links have a positive connotation, such as endorsement and trust, are
characterized by assortative mixing by degree, networks in which links have a
negative connotation, such as disapproval and distrust, are characterized by
disassortative patterns. We introduce a class of simple theoretical models to
analyze the interplay between network topology and the superimposed structure
based on the sign of links. Results uncover the conditions that underpin the
emergence of the patterns observed in the data, namely the assortativity of
positive subnetworks and the disassortativity of negative ones. We discuss the
implications of our study for the analysis of signed complex networks.
