I am currently trying to get a list of all referenced Twitter profiles in a database of Tweets in R. I already segmented each Tweet into a list of words (as string) and now I want to look up each value, that starts with "@" and save it (or the list if there is multiple references) into a new column of the database.

Data Sample:

@medieninsider Was meinen Sie, woher der zitierte Ausschnitt stammt?