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- from __future__ import unicode_literals
- import math
- def idf(posting, document_count):
- """A function to calculate the inverse document frequency for a posting.
- This is shared between the builder and the index.
- """
- documents_with_term = 0
- for field_name in posting:
- if field_name == "_index":
- continue
- documents_with_term += len(posting[field_name].keys())
- x = (document_count - documents_with_term + 0.5) / (documents_with_term + 0.5)
- return math.log(1 + abs(x))
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