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someBy

Test whether at least n elements along one or more ndarray dimensions pass a test implemented by a predicate function.

Installation

npm install @stdlib/ndarray-some-by

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 someBy = require( '@stdlib/ndarray-some-by' );

someBy( x, n[, options], predicate[, thisArg] )

Tests whether at least n elements along one or more ndarray dimensions pass a test implemented by a predicate function.

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

function predicate( value ) {
    return value > 0.0;
}

// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ] ], [ [ 3.0, 4.0 ] ], [ [ 0.0, 6.0 ] ] ] );
// returns <ndarray>

// Perform reduction:
var out = someBy( x, 2, predicate );
// returns <ndarray>

console.log( out.get() );
// => true

The function accepts the following arguments:

• x: input ndarray.
• n: number of elements which must pass the test implemented by a predicate function. May be either a scalar or an ndarray. Must be broadcast-compatible with the non-reduced dimensions of input ndarray. Must have an integer data type.
• options: function options (optional).
• predicate: predicate function.
• thisArg: predicate execution context (optional).

The function accepts the following options:

• dims: list of dimensions over which to perform a reduction.
• keepdims: boolean indicating whether the reduced dimensions should be included in the returned ndarray as singleton dimensions. Default: false.

By default, the function performs a reduction over all elements in a provided ndarray. To reduce specific dimensions, set the dims option.

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

function predicate( value ) {
    return value > 0.0;
}

// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ] ], [ [ 3.0, 4.0 ] ], [ [ 0.0, 6.0 ] ] ] );
// returns <ndarray>

var opts = {
    'dims': [ 0, 1 ]
};

// Perform reduction:
var out = someBy( x, 2, opts, predicate );
// returns <ndarray>

var v = ndarray2array( out );
// returns [ true, true ]

By default, the function returns an ndarray having a shape matching only the non-reduced dimensions of the input ndarray (i.e., the reduced dimensions are dropped). To include the reduced dimensions as singleton dimensions in the output ndarray, set the keepdims option to true.

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

function predicate( value ) {
    return value > 0.0;
}

// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ] ], [ [ 3.0, 4.0 ] ], [ [ 0.0, 6.0 ] ] ] );
// returns <ndarray>

var opts = {
    'dims': [ 0, 1 ],
    'keepdims': true
};

// Perform reduction:
var out = someBy( x, 2, opts, predicate );
// returns <ndarray>

var v = ndarray2array( out );
// returns [ [ [ true, true ] ] ]

To set the predicate function execution context, provide a thisArg.

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

function predicate( value ) {
    this.count += 1;
    return value > 0.0;
}

// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ] ], [ [ 3.0, 4.0 ] ], [ [ 0.0, 6.0 ] ] ] );
// returns <ndarray>

// Create a context object:
var ctx = {
    'count': 0
};

// Perform operation:
var out = someBy( x, 2, predicate, ctx );
// returns <ndarray>

var v = out.get();
// returns true

var count = ctx.count;
// returns 2

someBy.assign( x, n, out[, options], predicate[, thisArg] )

Tests whether at least n elements along one or more ndarray dimensions pass a test implemented by a predicate function and assigns results to a provided output ndarray.

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

function predicate( value ) {
    return value > 0.0;
}

// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ] ], [ [ 3.0, 4.0 ] ], [ [ 0.0, 6.0 ] ] ] );
// returns <ndarray>

// Create an output ndarray:
var y = empty( [], {
    'dtype': 'bool'
});

// Perform reduction:
var out = someBy.assign( x, 2, y, predicate );
// returns <ndarray>

var bool = ( out === y );
// returns true

var v = y.get();
// returns true

The function accepts the following arguments:

• x: input ndarray.
• n: number of elements which must pass the test implemented by a predicate function. May be either a scalar or an ndarray. Must be broadcast-compatible with the non-reduced dimensions of input ndarray. Must have an integer data type.
• out: output ndarray. The output ndarray must have a shape matching the non-reduced dimensions of the input ndarray.
• options: function options (optional).
• predicate: predicate function.
• thisArg: predicate execution context (optional).

The function accepts the following options:

• dims: list of dimensions over which to perform a reduction.

By default, the function performs a reduction over all elements in a provided ndarray. To reduce specific dimensions, set the dims option.

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

function predicate( value ) {
    return value > 0.0;
}

// Create an input ndarray:
var x = array( [ [ [ 1.0, 2.0 ] ], [ [ 3.0, 4.0 ] ], [ [ 0.0, 6.0 ] ] ] );
// returns <ndarray>

// Create an output ndarray:
var y = empty( [ 2 ], {
    'dtype': 'bool'
});

var opts = {
    'dims': [ 0, 1 ]
};

// Perform reduction:
var out = someBy.assign( x, 2, y, opts, predicate );

var bool = ( out === y );
// returns true

var v = ndarray2array( y );
// returns [ true, true ]

Notes

• The predicate function is provided the following arguments:

  • value: current array element.
  • indices: current array element indices.
  • arr: the input ndarray.

Examples

var discreteUniform = require( '@stdlib/random-base-discrete-uniform' ).factory;
var isEven = require( '@stdlib/assert-is-even' ).isPrimitive;
var ndarray2array = require( '@stdlib/ndarray-to-array' );
var scalar2ndarray = require( '@stdlib/ndarray-from-scalar' );
var fillBy = require( '@stdlib/ndarray-fill-by' );
var zeros = require( '@stdlib/ndarray-zeros' );
var someBy = require( '@stdlib/ndarray-some-by' );

var x = zeros( [ 2, 4, 5 ], {
    'dtype': 'float64'
});
x = fillBy( x, discreteUniform( 0, 10 ) );
console.log( ndarray2array( x ) );

var n = scalar2ndarray( 4, {
    'dtype': 'int8'
});
var y = someBy( x, n, isEven );
console.log( y.get() );

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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 © 2016-2025. The Stdlib Authors.