@stdlib/slice-base-seq2slice

Convert a subsequence string to a Slice object.

https://github.com/stdlib-js/slice-base-seq2slice

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base colon javascript ndarray node node-js nodejs python range sequence slice stdlib subseq subsequence

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Convert a subsequence string to a Slice object.

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Host: GitHub
Owner: stdlib-js
License: apache-2.0
Language: JavaScript
Default Branch: main
Homepage: https://github.com/stdlib-js/stdlib
Size: 446 KB

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base colon javascript ndarray node node-js nodejs python range sequence slice stdlib subseq subsequence

Created over 2 years ago · Last pushed 5 months ago

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We believe in a future in which the web is a preferred environment for numerical computation. To help realize this future, we've built stdlib. stdlib is a standard library, with an emphasis on numerical and scientific computation, written in JavaScript (and C) for execution in browsers and in Node.js.

The library is fully decomposable, being architected in such a way that you can swap out and mix and match APIs and functionality to cater to your exact preferences and use cases.

When you use stdlib, you can be absolutely certain that you are using the most thorough, rigorous, well-written, studied, documented, tested, measured, and high-quality code out there.

To join us in bringing numerical computing to the web, get started by checking us out on GitHub, and please consider financially supporting stdlib. We greatly appreciate your continued support!

seq2slice

Convert a subsequence string to a Slice object.

## Installation ```bash npm install @stdlib/slice-base-seq2slice ``` Alternatively, - To load the package in a website via a `script` tag without installation and bundlers, use the [ES Module][es-module] available on the [`esm`][esm-url] branch (see [README][esm-readme]). - If you are using Deno, visit the [`deno`][deno-url] branch (see [README][deno-readme] for usage intructions). - For use in Observable, or in browser/node environments, use the [Universal Module Definition (UMD)][umd] build available on the [`umd`][umd-url] branch (see [README][umd-readme]). The [branches.md][branches-url] file summarizes the available branches and displays a diagram illustrating their relationships. To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.

## Usage ```javascript var seq2slice = require( '@stdlib/slice-base-seq2slice' ); ``` #### seq2slice( str, len, strict ) Converts a subsequence string to a [`Slice`][@stdlib/slice/ctor] object, where `len` specifies the maximum number of elements allowed in the slice. ```javascript var s = seq2slice( ':5', 10, false ); // returns var v = s.start; // returns 0 v = s.stop; // returns 5 v = s.step; // returns 1 ``` A subsequence string has the following format: ```text :: ``` where - If an `increment` is not specified, the default increment is `1`. An increment of zero is **not** allowed. - The `start` index is **inclusive**. - The `stop` index is **exclusive**. - Both `start` and `stop` indices are _optional_. If not provided, `start` and `stop` default to index extremes. Which extremes correspond to which index depends on whether the `increment` is positive or negative. - Both `start` and `stop` can be negative; in which case, the corresponding index is resolved by subtracting the respective value from the provided length `len`. - Both `start` and `stop` can use the `end` keyword (e.g., `end-2::2`, `end-3:`, etc), which supports basic subtraction and division. - The `end` keyword resolves to the provided length `len`. Thus, `:-1` is equivalent to `:end-1`, `:-2` is equivalent to `:end-2`, and so on and so forth. The exception is when performing a division operation when the `increment` is less than zero; in which case, `end` is equal to `len-1` in order to preserve user expectations when `end/d` equals a whole number and slicing from right-to-left. The result from a division operation is **rounded down** to the nearest integer value. ```javascript var s = seq2slice( 'end:2:-1', 10, false ); // returns var v = s.start; // returns 9 v = s.stop; // returns 2 v = s.step; // returns -1 s = seq2slice( 'end-2:2:-1', 10, false ); // returns v = s.start; // returns 8 v = s.stop; // returns 2 v = s.step; // returns -1 s = seq2slice( 'end/2:2:-1', 10, false ); // returns v = s.start; // returns 4 v = s.stop; // returns 2 v = s.step; // returns -1 ``` The function returns an error object if provided an invalid subsequence string. ```javascript var s = seq2slice( '1:2:3:4', 10, false ); // returns { 'code': 'ERR_SLICE_INVALID_SUBSEQUENCE' } ``` When `strict` is `true`, the function returns an error object if a subsequence string resolves to a slice exceeding index bounds. ```javascript var s = seq2slice( '10:20', 10, true ); // returns { 'code': 'ERR_SLICE_OUT_OF_BOUNDS' } ``` A returned error object may have one of the following error codes: - **ERR_SLICE_INVALID_SUBSEQUENCE**: a subsequence string is invalid. - **ERR_SLICE_INVALID_INCREMENT**: a subsequence string must have a non-zero increment. - **ERR_SLICE_OUT_OF_BOUNDS**: a subsequence string resolves to a slice exceeding index bounds.

## Notes - When `len` is zero, the function always returns a Slice object equivalent to `0:0:`. - When `strict` is `false`, the resolved slice start is clamped to the slice index bounds (i.e., `[0, len)`). - When `strict` is `false`, the resolved slice end is upper bound clamped to `len` (i.e., one greater than the last possible index). - When the increment is negative, the resolved slice end value may be `null`, thus indicating that a non-empty slice should include the first index. - The function ensures that results satisfy the convention that `:n` combined with `n:` is equivalent to `:` (i.e., selecting all elements). This convention matches Python slice semantics, but diverges from the MATLAB convention where `:n` and `n:` overlap by one element. - Unlike MATLAB, but like Python, the subsequence string is upper-bound exclusive. For example, in Python, `0:2` corresponds to the sequence `{0,1}`. In MATLAB, `1:3` corresponds to `{1,2,3}`.

## Examples ```javascript var seq2slice = require( '@stdlib/slice-base-seq2slice' ); var s = seq2slice( ':', 5, false ); console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step ); // => 'start: 0. stop: 5. step: 1.' s = seq2slice( '2:', 5, false ); console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step ); // => 'start: 2. stop: 5. step: 1.' s = seq2slice( ':3', 5, false ); console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step ); // => 'start: 0. stop: 3. step: 1.' s = seq2slice( '2:4', 5, false ); console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step ); // => 'start: 2. stop: 4. step: 1.' s = seq2slice( '1:4:2', 5, false ); console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step ); // => 'start: 1. stop: 4. step: 2.' s = seq2slice( '2::2', 5, false ); console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step ); // => 'start: 2. stop: 5. step: 2.' s = seq2slice( ':-2', 5, false ); console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step ); // => 'start: 0. stop: 3. step: 1.' s = seq2slice( ':-1:2', 5, false ); console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step ); // => 'start: 0. stop: 4. step: 2.' s = seq2slice( '-4:-1:2', 5, false ); console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step ); // => 'start: 1. stop: 4. step: 2.' s = seq2slice( '-5:-1', 5, false ); console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step ); // => 'start: 0. stop: 4. step: 1.' s = seq2slice( '::-1', 5, false ); console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step ); // => 'start: 4. stop: null. step: -1.' s = seq2slice( ':0:-1', 5, false ); console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step ); // => 'start: 4. stop: 0. step: -1.' s = seq2slice( '3:0:-1', 5, false ); console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step ); // => 'start: 3. stop: 0. step: -1.' s = seq2slice( '-1:-4:-2', 5, false ); console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step ); // => 'start: 4. stop: 1. step: -2.' s = seq2slice( ':end', 5, false ); console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step ); // => 'start: 0. stop: 5. step: 1.' s = seq2slice( ':end-1', 5, false ); console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step ); // => 'start: 0. stop: 4. step: 1.' s = seq2slice( ':end/2', 5, false ); console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step ); // => 'start: 0. stop: 2. step: 1.' s = seq2slice( 'end/2::-1', 5, false ); console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step ); // => 'start: 2. stop: null. step: -1.' s = seq2slice( 'end-2::-1', 5, false ); console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step ); // => 'start: 3. stop: null. step: -1.' s = seq2slice( 'end/2:', 5, false ); console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step ); // => 'start: 2. stop: 5. step: 1.' ```

* * * ## Notice This package is part of [stdlib][stdlib], a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more. For more information on the project, filing bug reports and feature requests, and guidance on how to develop [stdlib][stdlib], see the main project [repository][stdlib]. #### Community [![Chat][chat-image]][chat-url] --- ## License See [LICENSE][stdlib-license]. ## Copyright Copyright © 2016-2025. The Stdlib [Authors][stdlib-authors].

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Standard library for JavaScript.

Citation (CITATION.cff)

cff-version: 1.2.0
title: stdlib
message: >-
  If you use this software, please cite it using the
  metadata from this file.

type: software

authors:
  - name: The Stdlib Authors
    url: https://github.com/stdlib-js/stdlib/graphs/contributors

repository-code: https://github.com/stdlib-js/stdlib
url: https://stdlib.io

abstract: |
  Standard library for JavaScript and Node.js.

keywords:
  - JavaScript
  - Node.js
  - TypeScript
  - standard library
  - scientific computing
  - numerical computing
  - statistical computing

license: Apache-2.0 AND BSL-1.0

date-released: 2016

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npmjs.org: @stdlib/slice-base-seq2slice

Convert a subsequence string to a Slice object.

Homepage: https://stdlib.io
License: Apache-2.0
Latest release: 0.2.2
published over 1 year ago

Versions: 5
Dependent Packages: 4
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Downloads: 347 Last month

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planeshifter rreusser stdlib-bot kgryte

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