Editing Array slicing (section)

==Details==
For "one-dimensional" (single-indexed) arrays{{snd}} vectors, sequences, strings etc.{{snd}} the most common slicing operation is extraction of zero or more consecutive elements. If we have a vector containing elements (2, 5, 7, 3, 8, 6, 4, 1), and want to create an array slice from the 3rd to the 6th elements, we get (7, 3, 8, 6). In [[programming language]]s 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 removes the need for that index. This feature can be used, for example, to extract one-dimensional slices (vectors in 3D, including rows, columns, and tubes<ref name="Zhang Aeron pp. 1511–1526">{{cite journal | last1=Zhang | first1=Zemin | last2=Aeron | first2=Shuchin | title=Exact Tensor Completion Using t-SVD | journal=IEEE Transactions on Signal Processing | publisher=Institute of Electrical and Electronics Engineers (IEEE) | volume=65 | issue=6 | date=2017-03-15 | issn=1053-587X | doi=10.1109/tsp.2016.2639466 | pages=1511–1526| doi-access=free | arxiv=1502.04689 | bibcode=2017ITSP...65.1511Z }}</ref>) 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''{{snd}} 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 [[transpose|transposition]], index reversal, subsampling, etc. For languages like [[C (programming language)|C]], where the indices always start at zero, the dope vector of an array with ''d'' indices has at least 1 + 2''d'' parameters. For languages that allow arbitrary lower bounds for indices, like [[Pascal programming language|Pascal]], the dope vector needs 1 + 3''d'' entries.

If the array abstraction does not support true negative indices (as the arrays of [[Ada (programming language)|Ada]] and [[Pascal (programming language)|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 indicates the second-to-last item, while in a 0-based system, it refers to the very last item.