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<!-- | ||
@license Apache-2.0 | ||
Copyright (c) 2023 The Stdlib Authors. | ||
Licensed under the Apache License, Version 2.0 (the "License"); | ||
you may not use this file except in compliance with the License. | ||
You may obtain a copy of the License at | ||
http://www.apache.org/licenses/LICENSE-2.0 | ||
Unless required by applicable law or agreed to in writing, software | ||
distributed under the License is distributed on an "AS IS" BASIS, | ||
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
See the License for the specific language governing permissions and | ||
limitations under the License. | ||
--> | ||
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# slice | ||
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> Return a read-only view of an input ndarray. | ||
<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. --> | ||
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<section class="intro"> | ||
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</section> | ||
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<!-- /.intro --> | ||
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<!-- Package usage documentation. --> | ||
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<section class="usage"> | ||
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## Usage | ||
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```javascript | ||
var slice = require( '@stdlib/ndarray/slice' ); | ||
``` | ||
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#### slice( x, ...slice\[, options] ) | ||
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Returns a **read-only** view of an input ndarray. | ||
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```javascript | ||
var Slice = require( '@stdlib/slice/ctor' ); | ||
var MultiSlice = require( '@stdlib/slice/multi' ); | ||
var ndarray = require( '@stdlib/ndarray/ctor' ); | ||
var ndarray2array = require( '@stdlib/ndarray/to-array' ); | ||
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var buffer = [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ]; | ||
var shape = [ 3, 2 ]; | ||
var strides = [ 2, 1 ]; | ||
var offset = 0; | ||
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var x = ndarray( 'generic', buffer, shape, strides, offset, 'row-major' ); | ||
// returns <ndarray> | ||
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var sh = x.shape; | ||
// returns [ 3, 2 ] | ||
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var arr = ndarray2array( x ); | ||
// returns [ [ 1.0, 2.0 ], [ 3.0, 4.0 ], [ 5.0, 6.0 ] ] | ||
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var s0 = new Slice( null, null, -2 ); | ||
var s1 = new Slice( null, null, -1 ); | ||
var s = new MultiSlice( s0, s1 ); | ||
// returns <MultiSlice> | ||
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var y = slice( x, s ); | ||
// returns <ndarray> | ||
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sh = y.shape; | ||
// returns [ 2, 2 ] | ||
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arr = ndarray2array( y ); | ||
// returns [ [ 6.0, 5.0 ], [ 2.0, 1.0 ] ] | ||
``` | ||
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The function accepts the following arguments: | ||
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- **x**: input ndarray. | ||
- **slice**: a [`MultiSlice`][@stdlib/slice/multi] instance, an array of slice arguments, or slice arguments as separate arguments. | ||
- **options**: function options. | ||
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The function supports three (mutually exclusive) means for providing slice arguments: | ||
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1. providing a single [`MultiSlice`][@stdlib/slice/multi] instance. | ||
2. providing a single array of slice arguments. | ||
3. providing slice arguments as separate arguments. | ||
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The following example demonstrates each invocation style returning equivalent results. | ||
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```javascript | ||
var Slice = require( '@stdlib/slice/ctor' ); | ||
var MultiSlice = require( '@stdlib/slice/multi' ); | ||
var ndarray = require( '@stdlib/ndarray/ctor' ); | ||
var ndarray2array = require( '@stdlib/ndarray/to-array' ); | ||
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var buffer = [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ]; | ||
var shape = [ 3, 2 ]; | ||
var strides = [ 2, 1 ]; | ||
var offset = 0; | ||
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var x = ndarray( 'generic', buffer, shape, strides, offset, 'row-major' ); | ||
// returns <ndarray> | ||
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var sh = x.shape; | ||
// returns [ 3, 2 ] | ||
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var arr = ndarray2array( x ); | ||
// returns [ [ 1.0, 2.0 ], [ 3.0, 4.0 ], [ 5.0, 6.0 ] ] | ||
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// 1. Using a MultiSlice: | ||
var s0 = new Slice( 1, null, 1 ); | ||
var s1 = new Slice( null, null, 1 ); | ||
var s = new MultiSlice( s0, s1 ); | ||
// returns <MultiSlice> | ||
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var y = slice( x, s ); | ||
// returns <ndarray> | ||
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sh = y.shape; | ||
// returns [ 2, 2 ] | ||
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arr = ndarray2array( y ); | ||
// returns [ [ 3.0, 4.0 ], [ 5.0, 6.0 ] ] | ||
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// 2. Using an array of slice arguments: | ||
y = slice( x, [ s0, s1 ] ); | ||
// returns <ndarray> | ||
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sh = y.shape; | ||
// returns [ 2, 2 ] | ||
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arr = ndarray2array( y ); | ||
// returns [ [ 3.0, 4.0 ], [ 5.0, 6.0 ] ] | ||
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// 3. Providing separate arguments: | ||
y = slice( x, s0, s1 ); | ||
// returns <ndarray> | ||
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sh = y.shape; | ||
// returns [ 2, 2 ] | ||
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arr = ndarray2array( y ); | ||
// returns [ [ 3.0, 4.0 ], [ 5.0, 6.0 ] ] | ||
``` | ||
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The function supports the following `options`: | ||
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- **strict**: boolean indicating whether to enforce strict bounds checking. | ||
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By default, the function throws an error when provided a slice which exceeds array bounds. To return an empty array when a slice exceeds array bounds, set the `strict` option to `false`. | ||
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```javascript | ||
var Slice = require( '@stdlib/slice/ctor' ); | ||
var MultiSlice = require( '@stdlib/slice/multi' ); | ||
var ndarray = require( '@stdlib/ndarray/ctor' ); | ||
var ndarray2array = require( '@stdlib/ndarray/to-array' ); | ||
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var buffer = [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ]; | ||
var shape = [ 3, 2 ]; | ||
var strides = [ 2, 1 ]; | ||
var offset = 0; | ||
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var x = ndarray( 'generic', buffer, shape, strides, offset, 'row-major' ); | ||
// returns <ndarray> | ||
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var sh = x.shape; | ||
// returns [ 3, 2 ] | ||
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var arr = ndarray2array( x ); | ||
// returns [ [ 1.0, 2.0 ], [ 3.0, 4.0 ], [ 5.0, 6.0 ] ] | ||
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var s0 = new Slice( 1, null, 1 ); | ||
var s1 = new Slice( 10, 20, 1 ); | ||
var s = new MultiSlice( s0, s1 ); | ||
// returns <MultiSlice> | ||
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var y = slice( x, s, { | ||
'strict': false | ||
}); | ||
// returns <ndarray> | ||
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sh = y.shape; | ||
// returns [ 2, 0 ] | ||
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arr = ndarray2array( y ); | ||
// returns [] | ||
``` | ||
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</section> | ||
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<!-- /.usage --> | ||
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<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. --> | ||
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<section class="notes"> | ||
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## Notes | ||
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- A **slice argument** must be either a [`Slice`][@stdlib/slice/ctor], an integer, `null`, or `undefined`. | ||
- The number of slice dimensions must match the number of array dimensions. Hence, if `x` is a zero-dimensional [`ndarray`][@stdlib/ndarray/ctor], then, if `s` is a [`MultiSlice`][@stdlib/slice/multi], `s` should be empty, and, if `s` is an array, `s` should not contain any slice arguments. Similarly, if `x` is a one-dimensional [`ndarray`][@stdlib/ndarray/ctor], then, if `s` is a [`MultiSlice`][@stdlib/slice/multi], `s` should have one slice dimension, and, if `s` is an array, `s` should contain a single slice argument. And so on and so forth. | ||
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</section> | ||
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<!-- /.notes --> | ||
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<!-- Package usage examples. --> | ||
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<section class="examples"> | ||
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## Examples | ||
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<!-- eslint no-undef: "error" --> | ||
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<!-- eslint-disable new-cap --> | ||
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```javascript | ||
var S = require( '@stdlib/slice/ctor' ); | ||
var E = require( '@stdlib/slice/multi' ); | ||
var array = require( '@stdlib/ndarray/array' ); | ||
var ndarray2array = require( '@stdlib/ndarray/to-array' ); | ||
var zeroTo = require( '@stdlib/array/base/zero-to' ); | ||
var slice = require( '@stdlib/ndarray/slice' ); | ||
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// Alias `null` to allow for more compact indexing expressions: | ||
var _ = null; | ||
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// Create a linear ndarray buffer: | ||
var buf = zeroTo( 27 ); | ||
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// Create an ndarray: | ||
var x = array( buf, { | ||
'shape': [ 3, 3, 3 ] | ||
}); | ||
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// Get each matrix... | ||
var s1 = E( 0, _, _ ); | ||
var y1 = slice( x, s1 ); | ||
// returns <ndarray> | ||
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var a1 = ndarray2array( y1 ); | ||
// returns [ [ 0, 1, 2 ], [ 3, 4, 5 ], [ 6, 7, 8 ] ] | ||
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var s2 = E( 1, _, _ ); | ||
var y2 = slice( x, s2 ); | ||
// returns <ndarray> | ||
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var a2 = ndarray2array( y2 ); | ||
// returns [ [ 9, 10, 11 ], [ 12, 13, 14 ], [ 15, 16, 17 ] ] | ||
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var s3 = E( 2, _, _ ); | ||
var y3 = slice( x, s3 ); | ||
// returns <ndarray> | ||
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var a3 = ndarray2array( y3 ); | ||
// returns [ [ 18, 19, 20 ], [ 21, 22, 23 ], [ 24, 25, 26 ] ] | ||
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// Reverse all elements: | ||
var s = S( _, _, -1 ); | ||
var s4 = E( s, s, s ); | ||
var y4 = slice( x, s4 ); | ||
// returns <ndarray> | ||
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var a4 = ndarray2array( y4 ); | ||
// returns [...] | ||
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// Get the second rows from each matrix: | ||
var s5 = E( _, 1, _ ); | ||
var y5 = slice( x, s5 ); | ||
// returns <ndarray> | ||
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var a5 = ndarray2array( y5 ); | ||
// returns [ [ 3, 4, 5 ], [ 12, 13, 14 ], [ 21, 22, 23 ] ] | ||
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// Get the second columns from each matrix: | ||
var s6 = E( _, _, 1 ); | ||
var y6 = slice( x, s6 ); | ||
// returns <ndarray> | ||
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var a6 = ndarray2array( y6 ); | ||
// returns [ [ 1, 4, 7 ], [ 10, 13, 16 ], [ 19, 22, 25 ] ] | ||
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// Use an alternative invocation style: | ||
var y7 = slice( x, _, _, 1 ); | ||
// returns <ndarray> | ||
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var a7 = ndarray2array( y7 ); | ||
// returns [ [ 1, 4, 7 ], [ 10, 13, 16 ], [ 19, 22, 25 ] ] | ||
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// Use an alternative invocation style: | ||
var y8 = slice( x, [ _, _, 1 ] ); | ||
// returns <ndarray> | ||
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var a8 = ndarray2array( y8 ); | ||
// returns [ [ 1, 4, 7 ], [ 10, 13, 16 ], [ 19, 22, 25 ] ] | ||
``` | ||
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</section> | ||
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<!-- /.examples --> | ||
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<!-- Section to include cited references. If references are included, add a horizontal rule *before* the section. Make sure to keep an empty line after the `section` element and another before the `/section` close. --> | ||
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<section class="references"> | ||
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</section> | ||
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<!-- /.references --> | ||
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<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. --> | ||
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<section class="related"> | ||
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</section> | ||
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<!-- /.related --> | ||
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<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. --> | ||
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<section class="links"> | ||
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[@stdlib/slice/ctor]: https://github.com/stdlib-js/stdlib | ||
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[@stdlib/slice/multi]: https://github.com/stdlib-js/stdlib | ||
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[@stdlib/ndarray/ctor]: https://github.com/stdlib-js/ndarray/tree/main/ctor | ||
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</section> | ||
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<!-- /.links --> |
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