Regarding csv files, I use pandas to read it. In your case, you should convert each tweet to a vector before loading it to dataloader.
This tutorial explains how to make a dataloader from csv file.
https://pytorch.org/tutorials/beginner/data_loading_tutorial.html 208
So basically, you have to define init_, len, and getitem functions for a data loader. In addition, your init should have the part of converting tweet to a vector.