nditerColumnEntries

Create an iterator which returns [index, column] pairs for each column in a matrix (or stack of matrices).

Installation

npm install @stdlib/ndarray-iter-column-entries

Usage

var nditerColumnEntries = require( '@stdlib/ndarray-iter-column-entries' );

nditerColumnEntries( x[, options] )

Returns an iterator which returns [index, column] pairs for each column in a matrix (or stack of matrices).

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

var x = array( [ [ [ 1, 2 ], [ 3, 4 ] ], [ [ 5, 6 ], [ 7, 8 ] ] ] );
// returns <ndarray>

var iter = nditerColumnEntries( x );

var v = iter.next().value;
// returns [...]

var idx = v[ 0 ];
// returns [ 0, null, 0 ]

var col = ndarray2array( v[ 1 ] );
// returns [ 1, 3 ]

v = iter.next().value;
// returns [...]

idx = v[ 0 ];
// returns [ 0, null, 1 ]

col = ndarray2array( v[ 1 ] );
// returns [ 2, 4 ]

// ...

The function accepts the following options:

• readonly: boolean indicating whether returned ndarray views should be read-only. In order to return writable ndarray views, the input ndarray must be writable. If the input ndarray is read-only, setting this option to false raises an exception. Default: true.

By default, the iterator returns ndarray views which are read-only. To return writable views, set the readonly option to false.

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

var x = array( [ [ [ 1, 2 ], [ 3, 4 ] ], [ [ 5, 6 ], [ 7, 8 ] ] ] );
// returns <ndarray>

var iter = nditerColumnEntries( x, {
    'readonly': false
});

var v = iter.next().value;
// returns [...]

var col = ndarray2array( v[ 1 ] );
// returns [ 1, 3 ]

v[ 1 ].set( 0, 10 );

col = ndarray2array( v[ 1 ] );
// returns [ 10, 3 ]

The returned iterator protocol-compliant object has the following properties:

• next: function which returns an iterator protocol-compliant object containing the next iterated value (if one exists) assigned to a value property and a done property having a boolean value indicating whether the iterator is finished.
• return: function which closes an iterator and returns a single (optional) argument in an iterator protocol-compliant object.

Notes

• Each returned index is a Cartesian index (i.e., an array of subscripts/dimension indices). A dimension index equal to null indicates that all values along the respective dimension are included in the returned ndarray.
• If an environment supports Symbol.iterator, the returned iterator is iterable.
• A returned iterator does not copy a provided ndarray. To ensure iterable reproducibility, copy the input ndarray before creating an iterator. Otherwise, any changes to the contents of input ndarray will be reflected in the returned iterator.
• In environments supporting Symbol.iterator, the function explicitly does not invoke an ndarray's @@iterator method, regardless of whether this method is defined.

Examples

var ndarray2array = require( '@stdlib/ndarray-to-array' );
var array = require( '@stdlib/ndarray-array' );
var zeroTo = require( '@stdlib/array-base-zero-to' );
var nditerColumnEntries = require( '@stdlib/ndarray-iter-column-entries' );

// Define an input array:
var x = array( zeroTo( 27 ), {
    'shape': [ 3, 3, 3 ]
});

// Create an iterator for returning [index, column] pairs:
var it = nditerColumnEntries( x );

// Perform manual iteration...
var v;
while ( true ) {
    v = it.next();
    if ( v.done ) {
        break;
    }
    console.log( v.value[ 0 ] );
    console.log( ndarray2array( v.value[ 1 ] ) );
}

See Also

• @stdlib/ndarray-iter/columns: create an iterator which iterates over each column in a matrix (or stack of matrices).
• @stdlib/ndarray-iter/entries: create an iterator which returns [index, value] pairs for each element in a provided ndarray.
• @stdlib/ndarray-iter/row-entries: create an iterator which returns [index, row] pairs for each row in a matrix (or stack of matrices).
• @stdlib/ndarray-slice: return a read-only 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.