Introduced on day 41
Bag-of-words
A text representation that records which words occur in a message and how often, ignoring their order; one column per vocabulary word.
In detail
The document-term matrix is sparse (most words are absent from most messages). Discarding order loses negation and syntax but keeps topical signal, which is often enough for routing and tagging. It is the starting point for TF-IDF and for LSA.