Label propagation in GraphChi by Danny Bickson.
From the post:
A few days ago I got a request from Jidong, from the Chinese Renren company to implement label propagation in GraphChi. The algorithm is very simple described here: Zhu, Xiaojin, and Zoubin Ghahramani. Learning from labeled and unlabeled data with label propagation. Technical Report CMU-CALD-02-107, Carnegie Mellon University, 2002.
The basic idea is that we start with a group of users that we have some information about the categories they are interested in. Following the weights in the social network, we propagate the label probabilities from the user seed node (the ones we have label information about) into the general social network population. After several iterations, the algorithm converges and the output is labels for the unknown nodes.
I assume there is more unlabeled data for topic maps than labeled data.
Depending upon your requirements, this could prove to be a useful technique for completing those unlabeled nodes.