Array Function

Applies a function to each array element.

Installation

$ npm install compute-array-function

For use in the browser, use browserify.

Usage

var arrayfun = require( 'compute-array-function' );

arrayfun( fcn, ...array[, options] )

Applies a function to each array element. Array arguments may be either generic arrays, typed arrays, or a mixture of both.

var arr = [ 1, 2, 3, 4, 5 ];

function add5( val ) {
	return val + 5;
}

var out = arrayfun( add5, arr );
// returns [ 6, 7, 8, 9, 10 ]

The function accepts the following options:

• dtype: output data type. Default: generic.
• out: boolean indicating whether an output array has been provided. Default: false.

By default, the output array is a generic array. To specify a different data type, set the dtype option (see compute-array-constructors for a list of acceptable data types).

var out = arrayfun( add5, arr, {
	'dtype': 'int8';
});
// return Int8Array( [6,7,8,9,10] )

By default, the function returns a new array. To mutate an array (e.g., when input values can be discarded or when optimizing memory usage), set the out option to true to indicate that an output array has been provided as the first array argument.

var out = [ 0, 0, 0, 0, 0 ];

arrayfun( add5, out, arr, {
	'out': 'true';
});
// returns [ 6, 7, 8, 9, 10 ]

// Works with typed output arrays, as well...
out = new Int8Array( 5 );

arrayfun( add5, out, arr, {
	'out': 'true';
});
// returns Int8Array( [6,7,8,9,10] )

===

Factory

The main exported function does not make any assumptions regarding the number of input arrays. To create a reusable array function where the number of input arrays is known, a factory method is provided.

arrayfun.factory( [fcn,] num[, options] )

Creates an apply function to apply a function to each array element.

var afun = arrayfun.factory( 2 );

function add( x, y ) {
	return x + y;
}

var arr1 = new Array( 5 ),
	arr2 = new Array( 5 );

for ( var i = 0; i < 5; i++ ) {
	arr1[ i ] = 5;
	arr2[ i ] = i + 5;
}
// arr1 = [ 5, 5, 5, 5, 5 ]
// arr2 = [ 5, 6, 7, 8, 9 ]

var out = afun( add, arr1, arr2 );
// returns [ 10, 11, 12, 13, 14 ]

An apply function may be provided during function creation.

var aadd = arrayfun.factory( add, 2 );

var out = aadd( arr1, arr2 );
// returns [ 10, 11, 12, 13, 14 ]

The function accepts the following options:

• dtype: output data type. Default: generic.

By default, the output array is a generic array. To specify a different data type, set the dtype option.

var aadd = arrayfun.factory( add, 2, {
	'dtype': 'int32';
});

var out = aadd( arr1, arr2 );
// returns Int32Array( [10,11,12,13,14] )

// ...and for all subsequent calls...
out = aadd( arr1, arr2 );
// returns Int32Array( [10,11,12,13,14] )

Note: a factory function always returns a new array.

===

Create

To facilitate using array functions within an application where input arguments are of known types and where memory management occurs externally, a method to create minimal array functions is provided.

arrayfun.create( [fcn,] num )

Creates an apply function to apply a function to each array element, where num is the number of input arrays excluding the output array.

var afcn = arrayfun.create( 2 ),
	out = new Array( 5 );

out = afcn( add, out, arr1, arr2 );
// returns [ 10, 11, 12, 13, 14 ]

function subtract( x, y ) {
	return x - y;
}

out = afcn( subtract, out, arr1, arr2 );
// returns [ 0, -1, -2, -3, -4 ]

An apply function may be provided during function creation.

var aadd = arrayfun.create( add, 2 );

var out = aadd( out, arr1, arr2 );
// returns [ 10, 11, 12, 13, 14 ]

===

Raw

Lower-level APIs are provided which forgo some of the guarantees of the above APIs, such as input argument validation. While use of the above APIs is encouraged in REPL environments, use of the lower-level interfaces may be warranted when arguments are of a known type or when performance is paramount.

arrayfun.raw( fcn, ...array[, options] )

Applies a function to each array element.

var arr = [ 0, 0, 0, 0, 0 ]

var out = arrayfun.raw( add5, arr );
// returns [ 5, 5, 5, 5, 5 ]

The function accepts the same options as the main exported function.

arrayfun.rawFactory( [fcn,] num[, options] )

Creates an apply function to apply a function to each array element.

var afun = arrayfun.rawFactory( 2 );

var out = afun( add, arr1, arr2 );
// returns [ 10, 11, 12, 13, 14 ]

The function accepts the same options as arrayfun.factory().

Notes

• Both factory methods, as well as the .create() method, use dynamic code evaluation. Beware when using these methods in the browser as they may violate your content security policy (CSP).

Examples

var arrayfun = require( 'compute-array-function' );

var arr1,
	arr2,
	out,
	i;

arr1 = new Array( 25 );
for ( i = 0; i < arr1.length; i++ ) {
	arr1[ i ] = i;
}

arr2 = new Int32Array( 25 );
for ( i = 0; i < arr2.length; i++ ) {
	arr2[ i ] = 5;
}

function add( x, y ) {
	return x + y;
}

out = arrayfun( add, arr1, arr2 );
console.log( out );

To run the example code from the top-level application directory,

$ node ./examples/index.js

Tests

Unit

Unit tests use the Mocha test framework with Chai assertions. To run the tests, execute the following command in the top-level application directory:

$ make test

All new feature development should have corresponding unit tests to validate correct functionality.

Test Coverage

This repository uses Istanbul as its code coverage tool. To generate a test coverage report, execute the following command in the top-level application directory:

$ make test-cov

Istanbul creates a ./reports/coverage directory. To access an HTML version of the report,

$ make view-cov

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License

MIT license.

Copyright

Copyright © 2015. The Compute.io Authors.