text: Large amounts of unprompted user-generated data on social media serve as distributed sensors 
  that better reﬂect public opinion [50] and oﬀer researchers more accurate insight into the associations 
  of concepts in people’s minds [51]. In particular, hashtags, a unique mechanism of social media, 
  provide researchers with an unprecedented chance to accurately extract the public cognitive framework 
  contained in texts. To inform or comment [52], social media users attach user-generated tagging with 
  a hash character “#” to anchor the keywords of their tweet and classify the tweet to a unifying topic, 
  and other users can view hashtags as beacons to follow speciﬁc topics and join collective discussions. 
  As a communicative marker, hashtags have been used in a wide range of cases [53] and have contributed 
  considerably to conversations and social participation [54,55]. In addition to the function as a topical 
  signiﬁer [56], social scientists noted that hashtags can also represent the context of a tweet [57], ﬂag 
  an individual’s community membership [58], or indicate shared interests [59]. Several studies adopted 
  hashtags as frame markers for both content and sentiment analysis [60–65] to eliminate researchers’ 
  subjectivity in frame detection. 