How does the hash part in hash maps work?

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Published on 2010-04-14T12:28:31Z Indexed on 2010/04/14 12:43 UTC
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So there is this nice picture in the hash maps article on Wikipedia:

Everything clear so far, except for the hash function in the middle.

How can a function generate the right index from any string? Are the indexes integers in reality too? If yes, how can the function output 1 for John Smith, 2 for Lisa Smith, etc.?

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