countIf

Count the number of truthy elements along one or more ndarray dimensions.

Installation

npm install @stdlib/ndarray-count-if

Usage

var countIf = require( '@stdlib/ndarray-count-if' );

countIf( x[, options], predicate[, thisArg] )

Counts the number of truthy elements along one or more ndarray dimensions.

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

function clbk( 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 = countIf( x, clbk );
// returns <ndarray>[ 5 ]

The function accepts the following arguments:

• x: input ndarray.
• options: function options (optional).
• predicate: predicate function.
• thisArg: predicate function 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' );

function clbk( 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 opts = {
    'dims': [ 1, 2 ]
};
var out = countIf( x, opts, clbk );
// returns <ndarray>[ 2, 2, 1 ]

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' );

function clbk( 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 opts = {
    'dims': [ 1, 2 ],
    'keepdims': true
};
var out = countIf( x, opts, clbk );
// returns <ndarray>[ [ [ 2 ] ], [ [ 2 ] ], [ [ 1 ] ] ]

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

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

function clbk( 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 reduction:
var out = countIf( x, clbk, ctx );
// returns <ndarray>[ 5 ]

var count = ctx.count;
// returns 6

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

Counts the number of truthy elements along one or more ndarray dimensions and assigns results to a provided output ndarray.

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

function clbk( 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': 'int32'
});

// Perform reduction:
var out = countIf.assign( x, y, clbk );
// returns <ndarray>[ 5 ]

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

The function accepts the following arguments:

• x: input ndarray.
• 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 function 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' );

function clbk( 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( [ 3 ], {
    'dtype': 'int32'
});

// Perform reduction:
var opts = {
    'dims': [ 1, 2 ]
};
var out = countIf.assign( x, y, opts, clbk );
// returns <ndarray>[ 2, 2, 1 ]

var bool = ( out === y );
// returns 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 bernoulli = require( '@stdlib/random-base-bernoulli' ).factory;
var ndarray2array = require( '@stdlib/ndarray-to-array' );
var fillBy = require( '@stdlib/ndarray-fill-by' );
var zeros = require( '@stdlib/ndarray-zeros' );
var isPositiveNumber = require( '@stdlib/assert-is-positive-number' ).isPrimitive;
var countIf = require( '@stdlib/ndarray-count-if' );

var x = zeros( [ 2, 4, 5 ], {
    'dtype': 'float64'
});
x = fillBy( x, bernoulli( 0.90 ) );
console.log( ndarray2array( x ) );

var y = countIf( x, isPositiveNumber );
console.log( 'countIf(x[:,:,:]) =' );
console.log( y.get() );

var opts = {
    'dims': [ 0 ],
    'keepdims': true
};
y = countIf( x, opts, isPositiveNumber );
console.log( 'countIf(x[:,j,k]) =' );
console.log( ndarray2array( y ) );

opts = {
    'dims': [ 1 ],
    'keepdims': true
};
y = countIf( x, opts, isPositiveNumber );
console.log( 'countIf(x[i,:,k]) =' );
console.log( ndarray2array( y ) );

opts = {
    'dims': [ 2 ],
    'keepdims': true
};
y = countIf( x, opts, isPositiveNumber );
console.log( 'countIf(x[i,j,:]) =' );
console.log( ndarray2array( y ) );

opts = {
    'dims': [ 0, 1 ],
    'keepdims': true
};
y = countIf( x, opts, isPositiveNumber );
console.log( 'countIf(x[:,:,k]) =' );
console.log( ndarray2array( y ) );

opts = {
    'dims': [ 0, 2 ],
    'keepdims': true
};
y = countIf( x, opts, isPositiveNumber );
console.log( 'countIf(x[:,j,:]) =' );
console.log( ndarray2array( y ) );

opts = {
    'dims': [ 1, 2 ],
    'keepdims': true
};
y = countIf( x, opts, isPositiveNumber );
console.log( 'countIf(x[i,:,:]) =' );
console.log( ndarray2array( y ) );

opts = {
    'dims': [ 0, 1, 2 ],
    'keepdims': true
};
y = countIf( x, opts, isPositiveNumber );
console.log( 'countIf(x[:,:,:]) =' );
console.log( ndarray2array( y ) );

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.