1. A computer-implemented method for clustering a plurality of users in social media, wherein the plurality of users each send messages, the computer-implemented method comprising the steps of: extracting a plurality of partial communities from the plurality of users, wherein the plurality of partial communities are based on relationships of companion messages, which are connected by sending, replying, or forwarding between users in the plurality of users; computing a first degree of similarity for showing a similarity of companion partial communities, wherein the companion partial communities are based on the relationship of users with other users, and wherein the first degree of similarity is based on a relationship of a user belonging to a first partial community with a user belonging to a second partial community; computing a second degree of similarity for showing a similarity of companion partial communities, wherein the second degree of similarity is based on words in the messages sent by users belonging to the first and second partial communities and so that the first degree of similarity is higher than a predetermined first threshold value; and creating an integrated community by integrating the companion partial communities so that the second degree of similarity is higher than a predetermined second threshold value.