A vector description encodes each data instance as a one-dimensional vector of numerical attributes, or features. A dataset then becomes a rank-2 tensor: samples form the first axis, and features form the second. section 2.2.8
Two concrete datasets
Represent each person by age, gender, and income; 100,000 people form a tensor with shape (100000, 3). Represent each document by word counts from a 20,000-word dictionary; 500 documents form shape (500, 20000). section 2.2.8
