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The most frequently used general-purpose implementation of an associative array is with a hash table: an array combined with a hash function that separates each key into a separate "bucket" of the array. The basic idea behind a hash table is that accessing an element of an array via its index is a simple, constant-time operation.
There is no standard implementation of associative arrays in C, but a 3rd-party library, C Hash Table, with BSD license, is available. [1] Another 3rd-party library, uthash, also creates associative arrays from C structures. A structure represents a value, and one of the structure fields serves as the key. [2]
In the hash table implementation of associative arrays, an array of length is partially filled with elements, where . A key x {\displaystyle x} is hashed using a hash function h {\displaystyle h} to compute an index location A [ h ( x ) ] {\displaystyle A[h(x)]} in the hash table, where h ( x ) < m {\displaystyle h(x)<m} .
In the programming language C++, unordered associative containers are a group of class templates in the C++ Standard Library that implement hash table variants. Being templates , they can be used to store arbitrary elements, such as integers or custom classes.
The disadvantage of association lists is that the time to search is O(), where n is the length of the list. [3] For large lists, this may be much slower than the times that can be obtained by representing an associative array as a binary search tree or as a hash table.
For example, a priority queue is often implemented as a heap, while an associative array is often implemented as a hash table, so these abstract types are often referred to by this preferred implementation, as a "heap" or a "hash", though this is incorrect conceptually.
In addition to support for vectorized arithmetic and relational operations, these languages also vectorize common mathematical functions such as sine. For example, if x is an array, then y = sin (x) will result in an array y whose elements are sine of the corresponding elements of the array x. Vectorized index operations are also supported.
an associative array; allows mapping from one data item (a key) to another (a value). Type of key must implement comparison operator < or custom comparator function must be specified; such comparison operator or comparator function must guarantee strict weak ordering, otherwise behavior is undefined. Typically implemented using a self-balancing ...