For: DNA microarray
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For: DNA microarray
In computer science an array is a data structure consisting of a group of elements that are accessed by indexing. In most programming languages each element has the same data type and the array occupies a contiguous area of storage.
Overview
Most programming languages have a built-in array data type, although what is called an array in the language documentation is sometimes really an associative array. Conversely, the contiguous storage kind of array discussed here may alternatively be called a vector, list, or table.
Some programming languages support array programming (e.g., APL, newer versions of Fortran) which generalises operations and functions to work transparently over arrays as they do with scalars, instead of requiring looping over array members.
Multi-dimensional arrays are accessed using more than one index: one for each dimension. Multidimensional indexing reduced to a lesser number of dimensions, for example, a two-dimensional array with consisting of 6 and 5 elements respectively could be represented using a one-dimensional array of 30 elements.
Arrays can be classified as fixed-sized arrays (sometimes known as static arrays) whose size cannot change once their storage has been allocated, or dynamic arrays, which can be resized.
Properties
Arrays permit constant time (O(1)) random access to individual elements, which is optimal, but moving elements requires time proportional to the number of elements moved. On actual hardware, the presence of e.g. caches can make sequential iteration over an array noticeably faster than random access — a consequence of arrays having good locality of reference because their elements occupy contiguous memory locations — but this does not change the asymptotic complexity of access. Likewise, there are often facilities (such as memcpy) which can be used to move contiguous blocks of array elements faster than one can do through individual element access, but that does not change the asymptotic complexity either.
Memory-wise, arrays are compact data structures with no per-element overhead. There may be a per-array overhead, e.g. to store index bounds, but this is language-dependent. It can also happen that elements stored in an array require less memory than the same elements stored in individual variables, because several array elements can be stored in a single word; such arrays are often called packed arrays.
Properties in comparison
Dynamic arrays have similar characteristics to arrays, but can grow. The price for this is a memory overhead, due to elements being allocated but not used. With a constant per-element bound on the memory overhead, dynamic arrays can grow in constant amortized time per element.
