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  2. Count-distinct problem - Wikipedia

    en.wikipedia.org/wiki/Count-distinct_problem

    To handle the bounded storage constraint, streaming algorithms use a randomization to produce a non-exact estimation of the distinct number of elements, . State-of-the-art estimators hash every element into a low-dimensional data sketch using a hash function, (). The different techniques can be classified according to the data sketches they store.

  3. Array (data type) - Wikipedia

    en.wikipedia.org/wiki/Array_(data_type)

    An array data structure can be mathematically modeled as an abstract data structure (an abstract array) with two operations get(A, I): the data stored in the element of the array A whose indices are the integer tuple I. set(A, I, V): the array that results by setting the value of that element to V. These operations are required to satisfy the ...

  4. Comparison of programming languages (array) - Wikipedia

    en.wikipedia.org/wiki/Comparison_of_programming...

    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.

  5. Counting - Wikipedia

    en.wikipedia.org/wiki/Counting

    Number blocks, which can be used for counting. Counting is the process of determining the number of elements of a finite set of objects; that is, determining the size of a set. . The traditional way of counting consists of continually increasing a (mental or spoken) counter by a unit for every element of the set, in some order, while marking (or displacing) those elements to avoid visiting the ...

  6. Bit array - Wikipedia

    en.wikipedia.org/wiki/Bit_array

    The array elements may be aligned— each element begins on a byte or word boundary— or unaligned— elements immediately follow each other with no padding. PL/pgSQL and PostgreSQL's SQL support bit strings as native type. There are two SQL bit types: bit(n) and bit varying(n), where n is a positive integer. [8]

  7. Zero-based numbering - Wikipedia

    en.wikipedia.org/wiki/Zero-based_numbering

    To illustrate, suppose a is the memory address of the first element of an array, and i is the index of the desired element. To compute the address of the desired element, if the index numbers count from 1, the desired address is computed by this expression: + (), where s is the size of each element. In contrast, if the index numbers count from ...

  8. Associative array - Wikipedia

    en.wikipedia.org/wiki/Associative_array

    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.

  9. Pairing function - Wikipedia

    en.wikipedia.org/wiki/Pairing_function

    More generally, a pairing function on a set is a function that maps each pair of elements from into an element of , such that any two pairs of elements of are associated with different elements of , [5] [a] or a bijection from to .