SIMPLE PRESENT TENSE ASSOCIATIVE ARRAY

Associative array
An associative array (also associative container, map, mapping, dictionary, finite map, and in query-processing an index or index file) is an abstract data type composed of a collection of unique keys and a collection of values, where each key is associated with one value (or set of values). The operation of finding the value associated with a key is called a lookup or indexing, and this is the most important operation supported by an associative array. The relationship between a key and its value is sometimes called a mapping or binding. For example, if the value associated with the key "bob" is 7, we say that our array maps "bob" to 7. Associative arrays are very closely related to the mathematical concept of a function with a finite domain. As a consequence, a common and important use of associative arrays is in memoization.
From the perspective of a computer programmer, an associative array can be viewed as a generalization of an array. While a regular array maps an integer key (index) to a value of arbitrary data type, an associative array's keys can also be arbitrarily typed. In some programming languages, such as Python, the keys of an associative array do not even need to be of the same type.
Content-addressable memory (CAM) systems use a special type of computer memory to improve the performance of lookups in associative arrays and are used in specialized applications. Several supercomputers from the 1970s implemented CAM directly in hardware, and were known as associative computers.
Data structures for representing
Associative arrays are usually used when lookup is the most frequent operation. For this reason, implementations are usually designed to allow speedy lookup, at the expense of slower insertion and a larger storage footprint than other data structures (such as association lists).
Efficient representations
There are two main efficient data structures used to represent associative arrays, the hash table and the self-balancing binary search tree (such as a red-black tree or an AVL tree). Skip lists are also an alternative, though relatively new and not as widely used. B-trees (and variants) can also be used, and are commonly used when the associative array is too large to reside entirely in memory, for instance in a simple database.