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simple_bayes

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A Simple Bayes (a.k.a. Naive Bayes) implementation in Elixir.

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simple_bayes lib simple_bayes classifier models multinomial.ex
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lib/simple_bayes/classifier/models/multinomial.ex 

defmodule SimpleBayes.Classifier.Model.Multinomial do

  alias SimpleBayes.{Accumulator, MapMath, TfIdf}



  def probability_of(categories_map, cat_tokens_map, data) do

    likelihood = likelihood_of(categories_map, cat_tokens_map, data)

    prior      = MapMath.fraction(cat_tokens_map, data.tokens)



    likelihood * prior

  end



  defp likelihood_of(categories_map, cat_tokens_map, data) do

    tokens_map = Map.take(cat_tokens_map, Map.keys(categories_map))



    categories_map

    |> Map.merge(tokens_map)

    |> values_with_idf(data.tokens_per_training, data.trainings)

    |> Enum.reduce(1, &(&1 + &2))

    |> :math.log10()

  end



  defp values_with_idf(tokens_map, tokens_list, trainings_count) do

    Enum.map(tokens_map, fn ({token, weight}) ->

      TfIdf.call(weight, trainings_count, Accumulator.occurance(tokens_list, token))

    end)

  end

end