Кесу операциясы: Массивтен бөлік алу

Computer programming operation
the data structure operation
In computer programming, array slicing is an operation that extracts a subset of elements from an array and packages them as another array, possibly in a different dimension from the original. Common examples of array slicing are extracting a substring from a string of characters, the "ell" in "hello", extracting a row or column from a two dimensional array, or extracting a vector from a matrix. Depending on the programming language, an array slice can be made out of non consecutive elements. Also depending on the language, the elements of the new array may be aliased to (i. e., share memory with) those of the original array.

For "one dimensional" (single indexed) arrays vectors, sequence, strings etc. the most common slicing operation is extraction of zero or more consecutive elements. Thus, if we have a vector containing elements (2, 5, 7, 3, 8, 6, 4, 1), and we want to create an array slice from the 3rd to the 6th items, we get (7, 3, 8, 6). In programming languages that use a 0 based indexing scheme, the slice would be from index 2 to 5. Reducing the range of any index to a single value effectively eliminates that index. This feature can be used, for example, to extract one dimensional slices (vectors: in 3D, rows, columns, and tubes) or two dimensional slices (rectangular matrices) from a three dimensional array. However, since the range can be specified at run time, type checked languages may require an explicit (compile time) notation to actually eliminate the trivial indices. General array slicing can be implemented (whether or not built into the language) by referencing every array through a dope vector or descriptor a record that contains the address of the first array element, and then the range of each index and the corresponding coefficient in the indexing formula. This technique also allows immediate array transposition, index reversal, subsampling, etc. For languages like C, where the indices always start at zero, the dope vector of an array with d indices has at least 1 + 2d parameters. For languages that allow arbitrary lower bounds for indices, like Pascal, the dope vector needs 1 + 3d entries. If the array abstraction does not support true negative indices (as for example the arrays of Ada and Pascal do), then negative indices for the bounds of the slice for a given dimension are sometimes used to specify an offset from the end of the array in that dimension. In 1 based schemes, 1 generally would indicate the second to last item, while in a 0 based system, it would mean the very last item.

The concept of slicing was surely known even before the invention of compilers. Slicing as a language feature probably started with FORTRAN (1957), more as a consequence of non existent type and range checking than by design. The concept was also alluded to in the preliminary report for the IAL (ALGOL 58) in that the syntax allowed one or more indices of an array element (or, for that matter, of a procedure call) to be omitted when used as an actual parameter. Kenneth Iverson's APL (1957) had very flexible multi dimensional array slicing, which contributed much to the language's expressive power and popularity. ALGOL 68 (1968) introduced comprehensive multi dimension array slicing and trimming features. Array slicing facilities have been incorporated in several modern languages, such as Ada 2005, Cobra, D, Fortran 90, Go, Rust, Julia, MATLAB, Perl, Python, S Lang, Windows PowerShell and the mathematical/statistical languages GNU Octave, S and R.