map

Apply a callback function to elements in an input ndarray and assign results to elements in a new output ndarray.

Usage

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

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

Applies a callback function to elements in an input ndarray and assigns results to elements in a new output ndarray.

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

function scale( z ) {
    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 = map( x, scale );
// returns <ndarray>

var arr = ndarray2array( y );
// returns [ [ 20.0, 30.0, 40.0 ], [ 80.0, 90.0, 100.0 ] ]

The function accepts the following arguments:

  • x: input ndarray.
  • options: function options (optional).
  • fcn: callback to apply.
  • thisArg: callback execution context (optional).

The function accepts the following options:

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 scale( z ) {
    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 = map( x, opts, scale );
// returns <ndarray>

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

var arr = ndarray2array( y );
// returns [ [ 20.0, 30.0, 40.0 ], [ 80.0, 90.0, 100.0 ] ]

To set the callback 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 scale( z ) {
    this.count += 1;
    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 = map( x, scale, ctx );
// returns <ndarray>

var arr = ndarray2array( y );
// returns [ [ 20.0, 30.0, 40.0 ], [ 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.

    var Float64Array = require( '@stdlib/array/float64' );
var ndarray = require( '@stdlib/ndarray/ctor' );
var Complex128 = require( '@stdlib/complex/float64/ctor' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );

function toComplex( z ) {
    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 = map( x, opts, toComplex );
// returns <ndarray>

  • The function always returns an ndarray having the same shape and order as the input ndarray.

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

Examples

var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var abs = require( '@stdlib/math/base/special/abs' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );
var naryFunction = require( '@stdlib/utils/nary-function' );
var ndarray = require( '@stdlib/ndarray/ctor' );
var map = require( '@stdlib/ndarray/map' );

var buffer = discreteUniform( 10, -100, 100, {
    'dtype': 'generic'
});
var shape = [ 5, 2 ];
var strides = [ 2, 1 ];
var offset = 0;
var x = ndarray( 'generic', buffer, shape, strides, offset, 'row-major' );
console.log( ndarray2array( x ) );

var y = map( x, naryFunction( abs, 1 ) );
console.log( ndarray2array( y ) );

See Also

Did you find this page helpful?