8000 Curious for IDF calculations · Issue #4544 · scikit-learn/scikit-learn · GitHub
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l1th1um opened this issue Apr 8, 2015 · 2 comments
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Curious for IDF calculations #4544

l1th1um opened this issue Apr 8, 2015 · 2 comments

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@l1th1um
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l1th1um commented Apr 8, 2015

Hi,

I'm curious for IDF calculations (sklearn/feature_extraction/text.py) line 978

In 0.9, the formula for calculating IDF is log(n_samples/ (df + 1)), then in 16.0 the formula become log((n_samples + 1) / (df + 1)) + 1.

According to the Cornell SMART system, the formula of IDF is log((n_samples + 1) / (df + 1)). So, may I know the reason or reference paper for adding another +1 at the end of formula?

*smooth_idf = True
@jnothman
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jnothman commented Apr 8, 2015

See #4391, #2998

@l1th1um
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l1th1um commented Apr 8, 2015

thx

@l1th1um l1th1um closed this as completed Apr 8, 2015
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