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ndarray2fancy

Convert an ndarray to an object supporting fancy indexing.

A fancy ndarray is an ndarray which supports slicing via indexing expressions.

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

// Create a plain ndarray:
var buffer = [ 1, 2, 3, 4, 5, 6 ];
var x = new ndarray( 'generic', buffer, [ 6 ], [ 1 ], 0, 'row-major' );
// returns <ndarray>

// Convert to a fancy ndarray:
var y = ndarray2fancy( x );

// Select the first 3 elements:
var z = y[ ':3' ];
// returns <ndarray>

var arr = ndarray2array( z );
// returns [ 1, 2, 3 ]

// Select every other element, starting with the second element:
z = y[ '1::2' ];
// returns <ndarray>

arr = ndarray2array( z );
// returns [ 2, 4, 6 ]

// Reverse the array, starting with last element and skipping every other element:
z = y[ '::-2' ];
// returns <ndarray>

arr = ndarray2array( z );
// returns [ 6, 4, 2 ]

Installation

npm install @stdlib/ndarray-to-fancy

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 ndarray2fancy = require( '@stdlib/ndarray-to-fancy' );

ndarray2fancy( x[, options] )

Converts an ndarray to an object supporting fancy indexing.

console.log( 'TODO' );

The function supports the following options:

• cache: cache for resolving ndarray index objects. Must have a get method which accepts a single argument: a string identifier associated with an ndarray index.

  If an ndarray index associated with a provided identifier exists, the get method should return an object having the following properties:

  • data: the underlying index ndarray.
  • type: the index type. Must be either 'mask', 'bool', or 'int'.
  • dtype: the data type of the underlying ndarray.

  If an ndarray index is not associated with a provided identifier, the get method should return null.

  Default: ndindex.

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

By default, the function returns a fancy ndarray which does not enforce strict bounds checking. For example,

console.log( 'TODO' );

To enforce strict bounds checking, set the strict option to true.

console.log( 'TODO' );

ndarray2fancy.factory( [options] )

Returns a function for converting an ndarray to an object supporting fancy indexing.

var fcn = ndarray2fancy.factory();

console.log( 'TODO' );

The function supports the following options:

• cache: default cache for resolving ndarray index objects. Must have a get method which accepts a single argument: a string identifier associated with an ndarray index.

  If an ndarray index associated with a provided identifier exists, the get method should return an object having the following properties:

  • data: the underlying index ndarray.
  • type: the index type. Must be either 'mask', 'bool', or 'int'.
  • dtype: the data type of the underlying ndarray.

  If an ndarray index is not associated with a provided identifier, the get method should return null.

  Default: ndindex.

• strict: boolean indicating whether to enforce strict bounds checking by default. Default: false.

By default, the function returns a function which, by default, does not enforce strict bounds checking. For example,

var fcn = ndarray2fancy.factory();

console.log( 'TODO' );

To enforce strict bounds checking by default, set the strict option to true.

var fcn = ndarray2fancy.factory({
    'strict': true
});

console.log( 'TODO' );

The returned function supports the same options as above. When the returned function is provided option values, those values override the factory method defaults.

ndarray2fancy.idx( x[, options] )

Wraps a provided ndarray as an ndarray index object.

console.log( 'TODO' );

For documentation and usage, see ndindex.

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Notes

• A fancy ndarray shares the same data as the provided input ndarray. Hence, any mutations to the returned ndarray will affect the underlying input ndarray and vice versa.
• For operations returning a new ndarray (e.g., when slicing or invoking an instance method), a fancy ndarray returns a new fancy ndarray having the same configuration as specified by options.
• A fancy ndarray supports indexing using positive and negative integers (both numeric literals and strings), Slice and MultiSlice instances, subsequence expressions, and index arrays (boolean, mask, and integer).
• A fancy ndarray supports all properties and methods of the input ndarray, and, thus, a fancy ndarray can be consumed by any API which supports ndarray-like objects.
• Indexing expressions provide a convenient and powerful means for creating and operating on ndarray views; however, their use does entail a performance cost. Indexing expressions are best suited for interactive use (e.g., in the REPL) and scripting. For performance critical applications, prefer equivalent functional APIs supporting ndarray-like objects.
• In older JavaScript environments which do not support Proxy objects, the use of indexing expressions is not supported.

Bounds Checking

// TODO: see array/to-fancy

Broadcasting

// TODO: see array/to-fancy

Casting

// TODO: see array/to-fancy

---

Examples

var S = require( '@stdlib/slice-ctor' );
var E = require( '@stdlib/slice-multi' );
var toArray = require( '@stdlib/ndarray-to-array' );
var ndarray = require( '@stdlib/ndarray-ctor' );
var ndarray2fancy = require( '@stdlib/ndarray-to-fancy' );

var buffer = [
    1, 2,
    3, 4,  // 0
    5, 6,  // 1
    7, 8,  // 2
    9, 10
];
var shape = [ 3, 2 ];
var strides = [ 2, 1 ];
var offset = 2;

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

// Convert to a fancy ndarray:
var y = ndarray2fancy( x );

// Access an ndarray property:
var ndims = y.ndims;
// returns 2

// Retrieve an ndarray element:
var v = y.get( 2, 1 );
// returns 8

// Set an ndarray element:
y.set( 2, 1, 20 );
v = y.get( 2, 1 );
// returns 20

// Create an alias for `undefined` for more concise slicing expressions:
var _ = void 0;

// Create a multi-dimensional slice:
var s = E( S(0,_,2), _ );
// returns <MultiSlice>

// Use the slice to create a view on the original ndarray:
var y1 = y[ s ];
console.log( toArray( y1 ) );
// => [ [ 3, 4 ], [ 7, 20 ] ]

// Use alternative syntax:
var y2 = y[ [ S(0,_,2), _ ] ];
console.log( toArray( y2 ) );
// => [ [ 3, 4 ], [ 7, 20 ] ]

// Use alternative syntax:
var y3 = y[ '0::2,:' ];
console.log( toArray( y3 ) );
// => [ [ 3, 4 ], [ 7, 20 ] ]

// Flip dimensions:
var y4 = y[ [ S(_,_,-2), S(_,_,-1) ] ];
console.log( toArray( y4 ) );
// => [ [ 20, 7 ], [ 4, 3 ] ]

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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 © 2016-2024. The Stdlib Authors.