someBy

Test whether at least n elements in an ndarray pass a test implemented by a predicate function.

Installation

npm install @stdlib/ndarray-base-some-by

Usage

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

someBy( arrays, predicate[, thisArg ] )

Tests whether at least n elements in an ndarray pass a test implemented by a predicate function.

var Float64Array = require( '@stdlib/array-float64' );
var scalar2ndarray = require( '@stdlib/ndarray-from-scalar' );

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

// Create a data buffer:
var xbuf = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 0.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ] );

// Define the shape of the input array:
var shape = [ 3, 1, 2 ];

// Define the array strides:
var sx = [ 4, 4, 1 ];

// Define the index offset:
var ox = 0;

// Create the input ndarray-like object:
var x = {
    'dtype': 'float64',
    'data': xbuf,
    'shape': shape,
    'strides': sx,
    'offset': ox,
    'order': 'row-major'
};

// Define the success criterion:
var n = scalar2ndarray( 3, {
    'dtype': 'generic'
});

// Test elements:
var out = someBy( [ x, n ], predicate );
// returns true

The function accepts the following arguments:

• arrays: array-like object containing an input ndarray and a zero-dimensional ndarray specifying the minimum number of elements in the input ndarray that must satisfy the predicate function.
• predicate: predicate function.
• thisArg: predicate function execution context (optional).

Each provided ndarray should be an object with the following properties:

• dtype: data type.
• data: data buffer.
• shape: dimensions.
• strides: stride lengths.
• offset: index offset.
• order: specifies whether an ndarray is row-major (C-style) or column major (Fortran-style).

The predicate function is provided the following arguments:

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

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

var Float64Array = require( '@stdlib/array-float64' );
var scalar2ndarray = require( '@stdlib/ndarray-from-scalar' );

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

// Create a data buffer:
var xbuf = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ] );

// Define the shape of the input array:
var shape = [ 3, 1, 2 ];

// Define the array strides:
var sx = [ 4, 4, 1 ];

// Define the index offset:
var ox = 0;

// Create the input ndarray-like object:
var x = {
    'dtype': 'float64',
    'data': xbuf,
    'shape': shape,
    'strides': sx,
    'offset': ox,
    'order': 'row-major'
};

// Define the success criterion:
var n = scalar2ndarray( 6, {
    'dtype': 'generic'
});

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

// Test elements:
var out = someBy( [ x, n ], predicate, ctx );
// returns true

var count = ctx.count;
// returns 6

Notes

• For very high-dimensional ndarrays which are non-contiguous, one should consider copying the underlying data to contiguous memory before performing the operation in order to achieve better performance.

Examples

var discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var scalar2ndarray = require( '@stdlib/ndarray-from-scalar' );
var ndarray2array = require( '@stdlib/ndarray-base-to-array' );
var someBy = require( '@stdlib/ndarray-base-some-by' );

function predicate( value ) {
    return value > 0;
}

var x = {
    'dtype': 'generic',
    'data': discreteUniform( 10, -2, 10, {
        'dtype': 'generic'
    }),
    'shape': [ 5, 2 ],
    'strides': [ 2, 1 ],
    'offset': 0,
    'order': 'row-major'
};
console.log( ndarray2array( x.data, x.shape, x.strides, x.offset, x.order ) );

var n = scalar2ndarray( 5, {
    'dtype': 'generic'
});

var out = someBy( [ x, n ], predicate );
console.log( out );

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 © 2016-2026. The Stdlib Authors.