Classify tweets by topic
Since there are no predefined topics, the task is unsupervised: the goal is to group tweets which are semantically similar together (as opposed to classification, which requires training a model to predict among specific classes).
The standard unsupervised approach is topic modelling. In the traditional LDA approach, a topic model groups the documents into clusters and also provides the probability of a word given a topic, so a list of &quot;top words&quot; by topic can be extracted from the model. LDA requires the number of topics as input parameter but Hierarchical Dirichlet Processes can be used to avoid this issue (it's less common however).