22 lines
653 B
JavaScript
22 lines
653 B
JavaScript
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/**
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* A function to calculate the inverse document frequency for
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* a posting. This is shared between the builder and the index
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*
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* @private
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* @param {object} posting - The posting for a given term
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* @param {number} documentCount - The total number of documents.
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*/
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lunr.idf = function (posting, documentCount) {
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var documentsWithTerm = 0
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for (var fieldName in posting) {
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if (fieldName == '_index') continue // Ignore the term index, its not a field
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documentsWithTerm += Object.keys(posting[fieldName]).length
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}
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var x = (documentCount - documentsWithTerm + 0.5) / (documentsWithTerm + 0.5)
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return Math.log(1 + Math.abs(x))
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}
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