TF-IDF

• TF-IDF is used to find the importance of a word in multiple documents
• TF = Term Frequency
  • number of times the word is in a document
• IDF = Inverse Document Frequency
  • how relevant that term is across all documents
• TF-IDF is the product of TF and IDF

[!def] TF-IDF
$$
TF-IDF(w) = \frac{count_{word ; w}\text{ in a doc }}{\text{total # of words in a doc}} log \frac{\text{# of documents with word w}}{\text{Total # of docs}}
$$

• TF-IDF can be used as Word Embedding also, by replacing $1$ in one-hot vector by the TF-IDF score.