Consider a document-term matrix, where tfij is the frequency of the ith word (term) in the jth document and m is the number of documents. Consider the variable transformation that is defined by

where dfi is the number of documents in which the ith term appears and is known as the document frequency of the term. This transformation is known as the inverse document frequency transformation.
(a) What is the effect of this transformation if a term occurs in one document? In every document?
(b) What might be the purpose of this transformation?

Transcribed Image Text:

7m 2 10