IDF Score

A IDF Score is non-negative real numeric score from an IDF function.

• Context:
  • It can range from being a [math]\displaystyle{ 0 }[/math] (when every multiset contains the member) to [math]\displaystyle{ \log(\mid C \mid) }[/math] (when only one multiset contains the member).
  • It can be a member of an IDF Vector (or an IDF matrix).
• Example(s):
  • [math]\displaystyle{ 0 }[/math], when every multiset contains the member.
  • [math]\displaystyle{ 2.301... }[/math], for [math]\displaystyle{ \operatorname{idf}(``\text{quaint}'', \text{Newsgroups 20 corpus}) }[/math], i.e. [math]\displaystyle{ \log(200) \equiv \log(\frac{8,000}{40}) }[/math], if the word quaint is contained in 40 documents from a corpus with 8,000 documents.
  • [math]\displaystyle{ \log(\mid C \mid) }[/math], when only one multiset contains the member.
  • …
• Counter-Example(s):
  • tf-idf Score,
  • PMI Score.
• See: TF Score, Vocabulary Member.

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