sliceDimension

Return a read-only view of an input ndarray when sliced along a specified dimension.

Installation

npm install @stdlib/ndarray-slice-dimension

Alternatively,

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If you are using Deno, visit the deno branch (see README for usage intructions).
For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

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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

var sliceDimension = require( '@stdlib/ndarray-slice-dimension' );

sliceDimension( x, dim, slice[, options] )

Returns a read-only view of an input ndarray when sliced along a specified dimension.

var Slice = require( '@stdlib/slice-ctor' );
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 s = new Slice( null, null, -1 );
// returns <Slice>

var y = sliceDimension( x, 0, s );
// returns <ndarray>

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

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

The function accepts the following arguments:

x: input ndarray.
dim: index of dimension along which to slice. If provided an integer less than zero, the dimension index is resolved relative to the last dimension, with the last dimension corresponding to the value -1.
slice: a Slice instance, null, undefined, or an integer. If provided null or undefined, the argument is equivalent to new Slice() (i.e., the returned view should include all elements along a specified dimension). If provided an integer less than zero, the corresponding element along the specified dimension is resolved relative to the last element along that dimension. For negative integers, the last element corresponds to the value -1.
options: function options.

The function supports the following options:

strict: boolean indicating whether to enforce strict bounds checking.

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.

var Slice = require( '@stdlib/slice-ctor' );
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 s = new Slice( 10, 20, 2 );
// returns <Slice>

var y = sliceDimension( x, 1, s, {
    'strict': false
});
// returns <ndarray>

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

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

Examples

var S = require( '@stdlib/slice-ctor' );
var array = require( '@stdlib/ndarray-array' );
var ndarray2array = require( '@stdlib/ndarray-to-array' );
var zeroTo = require( '@stdlib/array-base-zero-to' );
var sliceDimension = require( '@stdlib/ndarray-slice-dimension' );

// Alias `null` to allow for more compact indexing expressions:
var _ = null;

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

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

// Get each matrix...
var y1 = sliceDimension( x, 0, 0 );
// returns <ndarray>

var a1 = ndarray2array( y1 );
// returns [ [ 0, 1, 2 ], [ 3, 4, 5 ], [ 6, 7, 8 ] ]

var y2 = sliceDimension( x, 0, 1 );
// returns <ndarray>

var a2 = ndarray2array( y2 );
// returns [ [ 9, 10, 11 ], [ 12, 13, 14 ], [ 15, 16, 17 ] ]

var y3 = sliceDimension( x, 0, 2 );
// returns <ndarray>

var a3 = ndarray2array( y3 );
// returns [ [ 18, 19, 20 ], [ 21, 22, 23 ], [ 24, 25, 26 ] ]

// Reverse the matrix order:
var s = S( _, _, -1 );
var y4 = sliceDimension( x, 0, s );
// returns <ndarray>

var a4 = ndarray2array( y4 );
// returns [...]

// Get the second rows from each matrix:
var y5 = sliceDimension( x, 1, 1 );
// returns <ndarray>

var a5 = ndarray2array( y5 );
// returns [ [ 3, 4, 5 ], [ 12, 13, 14 ], [ 21, 22, 23 ] ]

// Get the second columns from each matrix:
var y6 = sliceDimension( x, 2, 1 );
// returns <ndarray>

var a6 = ndarray2array( y6 );
// returns [ [ 1, 4, 7 ], [ 10, 13, 16 ], [ 19, 22, 25 ] ]

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.