  We examine the relationship between social structure and sentiment through
the analysis of a large collection of tweets about the Irish Marriage
Referendum of 2015. We obtain the sentiment of every tweet with the hashtags
#marref and #marriageref that was posted in the days leading to the referendum,
and construct networks to aggregate sentiment and use it to study the
interactions among users. Our results show that the sentiment of mention tweets
posted by users is correlated with the sentiment of received mentions, and
there are significantly more connections between users with similar sentiment
scores than among users with opposite scores in the mention and follower
networks. We combine the community structure of the two networks with the
activity level of the users and sentiment scores to find groups of users who
support voting `yes' or `no' in the referendum. There were numerous
conversations between users on opposing sides of the debate in the absence of
follower connections, which suggests that there were efforts by some users to
establish dialogue and debate across ideological divisions. Our analysis shows
that social structure can be integrated successfully with sentiment to analyse
and understand the disposition of social media users. These results have
potential applications in the integration of data and meta-data to study
opinion dynamics, public opinion modelling, and polling.
