sliceFrom

Return a read-only shifted view of an input ndarray.

Installation

npm install @stdlib/ndarray-slice-from

Usage

var sliceFrom = require( '@stdlib/ndarray-slice-from' );

sliceFrom( x, ...start[, options] )

Returns a read-only shifted view of an input ndarray.

var ndarray = require( '@stdlib/ndarray-ctor' );
var ndarray2array = require( '@stdlib/ndarray-to-array' );

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;

var x = ndarray( 'generic', buffer, shape, strides, offset, 'row-major' );
// returns <ndarray>

var sh = x.shape;
// returns [ 3, 2 ]

var arr = ndarray2array( x );
// returns [ [ 1.0, 2.0 ], [ 3.0, 4.0 ], [ 5.0, 6.0 ] ]

var y = sliceFrom( x, 1, null );
// returns <ndarray>

sh = y.shape;
// returns [ 2, 2 ]

arr = ndarray2array( y );
// returns [ [ 3.0, 4.0 ], [ 5.0, 6.0 ] ]

The function accepts the following arguments:

• x: input ndarray.
• start: an array of starting indices (inclusive) or starting indices (inclusive) as separate arguments. Each index must be either null, undefined, or an integer. A value of null or undefined indicates to include all elements along a corresponding dimension. A negative integer indicates to resolve a starting index relative to the last element along a corresponding dimension, with the last element having index -1.
• options: function options.

The function supports two (mutually exclusive) means for providing index arguments:

1. providing a single array of index arguments.
2. providing index arguments as separate arguments.

The following example demonstrates each invocation style returning equivalent results.

var ndarray = require( '@stdlib/ndarray-ctor' );
var ndarray2array = require( '@stdlib/ndarray-to-array' );

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;

var x = ndarray( 'generic', buffer, shape, strides, offset, 'row-major' );
// returns <ndarray>

var sh = x.shape;
// returns [ 3, 2 ]

var arr = ndarray2array( x );
// returns [ [ 1.0, 2.0 ], [ 3.0, 4.0 ], [ 5.0, 6.0 ] ]

// 1. Using an array of index arguments:
var y = sliceFrom( x, [ 1, null ] );
// returns <ndarray>

sh = y.shape;
// returns [ 2, 2 ]

arr = ndarray2array( y );
// returns [ [ 3.0, 4.0 ], [ 5.0, 6.0 ] ]

// 2. Providing separate arguments:
y = sliceFrom( x, 1, null );
// returns <ndarray>

sh = y.shape;
// returns [ 2, 2 ]

arr = ndarray2array( y );
// returns [ [ 3.0, 4.0 ], [ 5.0, 6.0 ] ]

The function supports the following options:

• strict: boolean indicating whether to enforce strict bounds checking.

By default, the function throws an error when provided an index argument which exceeds array bounds. To return an empty array when an index exceeds array bounds, set the strict option to false.

var ndarray = require( '@stdlib/ndarray-ctor' );
var ndarray2array = require( '@stdlib/ndarray-to-array' );

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;

var x = ndarray( 'generic', buffer, shape, strides, offset, 'row-major' );
// returns <ndarray>

var sh = x.shape;
// returns [ 3, 2 ]

var arr = ndarray2array( x );
// returns [ [ 1.0, 2.0 ], [ 3.0, 4.0 ], [ 5.0, 6.0 ] ]

var y = sliceFrom( x, null, 20, {
    'strict': false
});
// returns <ndarray>

sh = y.shape;
// returns [ 3, 0 ]

arr = ndarray2array( y );
// returns []

Notes

• An index argument must be either an integer, null, or undefined.
• The number of indices must match the number of array dimensions. Hence, if x is a zero-dimensional ndarray, then, if start is an array, start should not contain any index arguments. Similarly, if x is a one-dimensional ndarray, then, if start is an array, start should contain a single index argument. And so on and so forth.

Examples

var array = require( '@stdlib/ndarray-array' );
var ndarray2array = require( '@stdlib/ndarray-to-array' );
var zeroTo = require( '@stdlib/array-base-zero-to' );
var sliceFrom = require( '@stdlib/ndarray-slice-from' );

// Create a linear ndarray buffer:
var buf = zeroTo( 27 );

// Create an ndarray:
var x = array( buf, {
    'shape': [ 3, 3, 3 ]
});

// Get the last two rows of each matrix:
var y1 = sliceFrom( x, null, 1, null );
// returns <ndarray>

var a1 = ndarray2array( y1 );
// returns [ [ [ 3, 4, 5 ], [ 6, 7, 8 ] ], [ [ 12, 13, 14 ], [ 15, 16, 17 ] ], [ [ 21, 22, 23 ], [ 24, 25, 26 ] ] ]

// Get the last two rows and columns of each matrix:
var y2 = sliceFrom( x, null, 1, 1 );
// returns <ndarray>

var a2 = ndarray2array( y2 );
// returns [ [ [ 4, 5 ], [ 7, 8 ] ], [ [ 13, 14 ], [ 16, 17 ] ], [ [ 22, 23 ], [ 25, 26 ] ] ]

// Get the last two 2x2 matrices:
var y3 = sliceFrom( x, 1, 1, 1 );
// returns <ndarray>

var a3 = ndarray2array( y3 );
// returns [ [ [ 13, 14 ], [ 16, 17 ] ], [ [ 22, 23 ], [ 25, 26 ] ] ]

See Also

• @stdlib/ndarray-array: multidimensional arrays.
• @stdlib/ndarray-ctor: multidimensional array constructor.
• @stdlib/ndarray-slice: return a read-only view of an input ndarray.
• @stdlib/ndarray-slice-dimension-from: return a read-only shifted view of an input ndarray along a specific dimension.
• @stdlib/ndarray-slice-to: return a read-only truncated view of an input ndarray.

Notice

This package is part of 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, see the main project repository.

Community

License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.