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TfIdf

This is a small library to calculate the most important words in given documents.

  • Tf: Term Frequency
  • Idf: Inverse Document Frequency

Tf (Term Frequency)

Formula:

Tf(d, t)
  • d: Document
  • t: Number of times term t appears in document d.

Df (Document Frequency)

The formula is:

Df(c, t)
  • c: Documents (corpus) of a given dataset.
  • t: Number of times term t appears in corpus c.

Inverse Document Frequency Formula:

1 / Df(c, t)

Tf.Idf

Formula is:

Tf.Idf(c, d, t) = Tf(d, t) / Df(c, t)

Tf.Idf Tweak 1

The problem with the simplest Tf.Idf approach is it gives very high score for very rare words so we need to "tweak" the formula. The simplest way would be adding log.

Formula:

Tf.Idf(c, d, t) = Tf(d, t) log (N / Df(c, t))
  • N: The number of total documents.

Stop words could be filtered out to get more accurate results. The stop words in stop_words.txt are from google.appengine.ext.search package.

License

Released under GPL3.