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first

Return a read-only view of the first element (or subarray) along one or more ndarray dimensions.

Installation

npm install @stdlib/ndarray-first

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• 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).

The branches.md 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

var first = require( '@stdlib/ndarray-first' );

first( x[, options] )

Returns a read-only view of the first element (or subarray) along one or more ndarray dimensions.

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

var x = array( [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ] );
// returns <ndarray>[ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ]

var v = first( x );
// returns <ndarray>[ 1.0 ]

The function accepts the following arguments:

• x: input ndarray.
• options: function options.

The function accepts the following options:

• dims: list of dimensions over which to perform the operation. If a dimension index is provided as an integer less than zero, the dimension index is resolved relative to the last dimension, with the last dimension corresponding to the value -1. By default, the function performs the operation over all dimensions.

To resolve the first element (or subarray) along one or more specified dimensions, provide a dims option:

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

var x = array( [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ] );
// returns <ndarray>[ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ]

// First column:
var v = first( x, {
    'dims': [ -1 ]
});
// returns <ndarray>[ 1.0, 3.0 ]

// First row:
v = first( x, {
    'dims': [ -2 ]
});
// returns <ndarray>[ 1.0, 2.0 ]

Notes

• The function always returns a read-only view. To convert a returned view to a writable ndarray, copy the contents to a new ndarray (e.g., via @stdlib/ndarray-copy).
• If provided an empty dims array, the function returns a read-only view of the input ndarray.

Examples

var uniform = require( '@stdlib/random-uniform' );
var ndarray2array = require( '@stdlib/ndarray-to-array' );
var first = require( '@stdlib/ndarray-first' );

var x = uniform( [ 3, 3, 3 ], -10.0, 10.0 );
console.log( ndarray2array( x ) );

// First scalar element:
var v = first( x );
console.log( v.get() );

// First columns along the innermost dimension:
v = first( x, {
    'dims': [ -1 ]
});
console.log( ndarray2array( v ) );

// First matrix along the outermost dimension:
v = first( x, {
    'dims': [ 0 ]
});
console.log( ndarray2array( v ) );

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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

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License

See LICENSE.

Copyright

Copyright © 2016-2026. The Stdlib Authors.