/mjolnir

A naive Bayes spam filter in Python

Primary LanguagePythonMIT LicenseMIT

mjolnir

Usage

python -m mjolnir phrase_to_test_goes_here

Example:

➜ poetry run python -m mjolnir enter for a chance to win big time
0.9981053489360789

Formula

The formula used is derived from Bayes' theorem:

Full equation

Where:

  • Pr(S|W) is the probability that a message is spam given that a word W is included in it
  • Pr(S) is the overall probability that a message is spam
  • Pr(W|S) is the probability that the word W appears in spam messages
  • Pr(H) is this overall probability that a message is ham
  • Pr(W|H) is the probability that the word W appears in ham messages

By assuming that the probabilities of a message being spam or ham are equal, we simplify the equation further

Assumptions

yields,

Reduced Equation

This is the exact equation used in the code to calculate the probability a word is spam or ham.

References

[1] Data taken from the National University of Singapore SMS Corpus

[2] The formula used in the code