filter

Usage

var filter = require( '@stdlib/ndarray/filter' );

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

Returns a shallow copy of an ndarray containing only those elements which pass a test implemented by a predicate function.

var Float64Array = require( '@stdlib/array/float64' );
var ndarray = require( '@stdlib/ndarray/ctor' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );

function predicate( z ) {
    return z > 6.0;
}

var buffer = 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 ] );
var shape = [ 2, 3 ];
var strides = [ 6, 1 ];
var offset = 1;

var x = ndarray( 'float64', buffer, shape, strides, offset, 'row-major' );
// returns <ndarray>

var y = filter( x, predicate );
// returns <ndarray>

var arr = ndarray2array( y );
// returns [ 8.0, 9.0, 10.0 ]

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:

• dtype: output ndarray data type. If not specified, the output ndarray data type is inferred from the input ndarray.
• order: index iteration order. By default, the function iterates over elements according to the layout order of the provided ndarray. Accordingly, for row-major input ndarrays, the last dimension indices increment fastest. For column-major input ndarrays, the first dimension indices increment fastest. To override the inferred order and ensure that indices increment in a specific manner, regardless of the input ndarray's layout order, explicitly set the iteration order. Note, however, that iterating according to an order which does not match that of the input ndarray may, in some circumstances, result in performance degradation due to cache misses. Must be either 'row-major' or 'column-major'.

By default, the output ndarray data type is inferred from the input ndarray. To return an ndarray with a different data type, specify the dtype option.

var Float64Array = require( '@stdlib/array/float64' );
var ndarray = require( '@stdlib/ndarray/ctor' );
var dtype = require( '@stdlib/ndarray/dtype' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );

function predicate( z ) {
    return z > 6.0;
}

var buffer = 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 ] );
var shape = [ 2, 3 ];
var strides = [ 6, 1 ];
var offset = 1;

var x = ndarray( 'float64', buffer, shape, strides, offset, 'row-major' );
// returns <ndarray>

var opts = {
    'dtype': 'float32'
};
var y = filter( x, opts, predicate );
// returns <ndarray>

var dt = dtype( y );
// returns 'float32'

var arr = ndarray2array( y );
// returns [ 8.0, 9.0, 10.0 ]

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

var Float64Array = require( '@stdlib/array/float64' );
var ndarray = require( '@stdlib/ndarray/ctor' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );

function predicate( z ) {
    this.count += 1;
    return z > 6.0;
}

var buffer = 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 ] );
var shape = [ 2, 3 ];
var strides = [ 6, 1 ];
var offset = 1;

var x = ndarray( 'float64', buffer, shape, strides, offset, 'row-major' );
// returns <ndarray>

var ctx = {
    'count': 0
};
var y = filter( x, predicate, ctx );
// returns <ndarray>

var arr = ndarray2array( y );
// returns [ 8.0, 9.0, 10.0 ]

var count = ctx.count;
// returns 6

The predicate function is provided the following arguments:

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