What is the formula and log base for idf?

To calculate tf-idf, we do:

tf*idf

tf=number of times word occurs in document

What is formula for idf and log base:

  1. Log(number of documents/number of documents containing the word)

  2. Log((1+number of documents)/(1+number of documents containing the word))

  3. 1+Log(number of documents/number of documents containing the word)

  4. 1+Log((1+number of documents)/(1+number of documents containing the word))

Topic search-engine tfidf

Category Data Science

1
answered at

There a a number of variation how to calculate inverse document frequency. Have a look at the wiki page (Tf-Idf) or scikit-learn's TfidfVetorizer class.

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