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About stdlib...

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filterMap

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Filter and map elements in an input ndarray to elements in a new output ndarray according to a callback function.

Usage

import filterMap from 'https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-filter-map@deno/mod.js';

filterMap( x[, options], fcn[, thisArg] )

Filters and maps elements in an input ndarray to elements in a new output ndarray according to a callback function.

import Float64Array from 'https://cdn.jsdelivr.net/gh/stdlib-js/array-float64@deno/mod.js';
import ndarray from 'https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-ctor@deno/mod.js';
import ndarray2array from 'https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-to-array@deno/mod.js';

function fcn( z ) {
    if ( z > 5.0 ) {
        return z * 10.0;
    }
}

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 = filterMap( x, fcn );
// returns <ndarray>

var arr = ndarray2array( y );
// returns [ 80.0, 90.0, 100.0 ]

The function accepts the following arguments:

  • x: input ndarray.
  • options: function options (optional).
  • fcn: callback function.
  • thisArg: callback 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 manor, 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.

import Float64Array from 'https://cdn.jsdelivr.net/gh/stdlib-js/array-float64@deno/mod.js';
import ndarray from 'https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-ctor@deno/mod.js';
import dtype from 'https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-dtype@deno/mod.js';
import ndarray2array from 'https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-to-array@deno/mod.js';

function fcn( z ) {
    if ( z > 5.0 ) {
        return z * 10.0;
    }
}

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 = filterMap( x, opts, fcn );
// returns <ndarray>

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

var arr = ndarray2array( y );
// returns [ 80.0, 90.0, 100.0 ]

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

import Float64Array from 'https://cdn.jsdelivr.net/gh/stdlib-js/array-float64@deno/mod.js';
import ndarray from 'https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-ctor@deno/mod.js';
import ndarray2array from 'https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-to-array@deno/mod.js';

function fcn( z ) {
    this.count += 1;
    if ( z > 5.0 ) {
        return z * 10.0;
    }
}

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 = filterMap( x, fcn, ctx );
// returns <ndarray>

var arr = ndarray2array( y );
// returns [ 80.0, 90.0, 100.0 ]

var count = ctx.count;
// returns 6

The callback function is provided the following arguments:

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

Notes

  • The function does not perform explicit casting (e.g., from a real-valued floating-point number to a complex floating-point number). Any such casting should be performed by a provided callback function.

    import Float64Array from 'https://cdn.jsdelivr.net/gh/stdlib-js/array-float64@deno/mod.js';
    import ndarray from 'https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-ctor@deno/mod.js';
    import Complex128 from 'https://cdn.jsdelivr.net/gh/stdlib-js/complex-float64-ctor@deno/mod.js';
    import ndarray2array from 'https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-to-array@deno/mod.js';
    
    function fcn( z ) {
        if ( z > 5.0 ) {
            return new Complex128( z, 0.0 );
        }
    }
    
    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': 'complex128'
    };
    var y = filterMap( x, opts, fcn );
    // returns <ndarray>
  • If a provided callback function returns undefined, the function skips the respective ndarray element. If the callback function returns a value other than undefined, the function stores the callback's return value in the output ndarray.

  • The function always returns a one-dimensional ndarray.

Examples

import discreteUniform from 'https://cdn.jsdelivr.net/gh/stdlib-js/random-array-discrete-uniform@deno/mod.js';
import ndarray2array from 'https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-to-array@deno/mod.js';
import array from 'https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-array@deno/mod.js';
import filterMap from 'https://cdn.jsdelivr.net/gh/stdlib-js/ndarray-filter-map@deno/mod.js';

function fcn( v ) {
    if ( v > 0 ) {
        return v * 100;
    }
}

var buffer = discreteUniform( 10, -100, 100, {
    'dtype': 'generic'
});
var x = array( buffer, {
    'shape': [ 5, 2 ],
    'dtype': 'generic'
});
console.log( ndarray2array( x ) );

var y = filterMap( x, fcn );
console.log( ndarray2array( y ) );

See Also

  • @stdlib/ndarray-filter: return a shallow copy of an ndarray containing only those elements which pass a test implemented by a predicate function.
  • @stdlib/ndarray-map: apply a callback to elements in an input ndarray and assign results to elements in a new output ndarray.
  • @stdlib/ndarray-reject: return a shallow copy of an ndarray containing only those elements which fail a test implemented by a predicate function.
  • @stdlib/ndarray-slice: return a read-only view of an input ndarray.

Notice

This package is part of stdlib, a standard library 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.

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License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.