I would argue that you have completely reversed the proper comparison; calling the data structure a hash confuses implementation and concept, while calling it an associative array focuses on the concept.

As Wikipedia says, an associative array is an abstract data type that maps a set of keys onto values. The analogy to an array is that arrays associate indexes with values, while associative arrays associate more general keys with values. So it is like an array, but with a more flexible choice of association. (Depending on the language and/or library, keys may even be arbitrary objects.) There are many ways to implement them. In fact the two Lisp examples you gave are valid (albeit inefficient) implementations!

The term "associative array" is used in many languages. You can see how ubiquitous the term is across languages by googling for associative array. When I did that, the top links were to the Wikipedia page I gave, then articles on PHP, JavaScript, Oracle PL/SQL, PHP again, an entry in a data structures dictionary, an article on C++ compilers, a Perl article, etc. Clearly the term is very well established in the broader programming world.

By contrast when we say hash we're referring to the implementation. Perl hashes are internally implemented using hash tables. (Common Lisp also has hash tables built in.) However there is no guarantee that Perl's hashes will always be so implemented. Perl has changed hashing algorithms in the past, and theoretically could switch to using a BTree at some point in the future. (Extremely unlikely though.)

In reply to Re^4: Associative array by tilly
in thread Associative array by gem555

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