Textual documents

What do text and images have in common? At first glance: very little. However, if we represent a sentence or a document as a matrix, then this matrix is not much different from an image matrix where each cell is a pixel. So, the next question is: how can we represent a piece of text as a matrix?

Well, it is pretty simple: each row of a matrix is a vector that represents a basic unit for the text. Of course, now we need to define what a basic unit is. A simple choice could be to say that the basic unit is a character. Another choice would be to say that a basic unit is a word, yet another choice is to aggregate similar words together and then denote each aggregation (sometimes called clustering or embedding) with a representative symbol.

Note that regardless of the specific choice adopted for our basic units, we need to have a 1:1 map from basic units into integer IDs so that a text can be seen as a matrix. For instance, if we have a document with 10 lines of...