Introduction to Information Retrieval
Introduction to Information Retrieval Introduction to Information Retrieval
Introduction to Information Retrieval Examples for idf • Compute idf t using the formula: term df t idf t calpurnia animal sunday fly under the 1 100 1000 10,000 100,000 1,000,000 6 4 3 2 1 0 24
Introduction to Information Retrieval Effect of idf on ranking • idf affects the ranking of documents for queries with at least two terms. • For example, in the query “arachnocentric line”, idf weighting increases the relative weight of ARACHNOCENTRIC and decreases the relative weight of LINE. • idf has little effect on ranking for one-term queries. 25
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<strong>Introduction</strong> <strong>to</strong> <strong>Information</strong> <strong>Retrieval</strong><br />
Examples for idf<br />
• Compute idf t using the formula:<br />
term df t idf t<br />
calpurnia<br />
animal<br />
sunday<br />
fly<br />
under<br />
the<br />
1<br />
100<br />
1000<br />
10,000<br />
100,000<br />
1,000,000<br />
6<br />
4<br />
3<br />
2<br />
1<br />
0<br />
24
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