signum

Signum function.

The Signum function is defined as

for any real number x.

Installation

$ npm install compute-signum

For use in the browser, use browserify.

Usage

var signum = require( 'compute-signum' );

signum( x[, options] )

Evaluates the signum function. x may be either a number, an array, a typed array, or a matrix. Values may include NaN, +infinity, and -infinity

var matrix = require( 'dstructs-matrix' ),
	data,
	mat,
	out,
	i;

out = signum( -10 );
// returns -1

out = signum( [ -10, -1, -0, 0, 1, 10 ] );
// returns [ -1, -1, 0, 0, 1, 1 ]

data = [ -2, 0, 2 ];
out = signum( data );
// returns [ -1, 0, 1 ]

data = new Float64Array( data );
out = signum( data );
// returns Int8Array( [ -1, 0, 1 ] )

data = new Float64Array( 6 );
for ( i = 0; i < 6; i++ ) {
	data[ i ] = i - 3;
}
mat = matrix( data, [3,2], 'float64' );
/*
	[ -3 -2
	  -1  0
	   1  2 ]
*/

out = signum( mat );
/*
	[ -1 -1
	  -1  0
	   1  1 ]
*/

The function accepts the following options:

• accessor: accessor function for accessing array values.
• copy: boolean indicating if the function should return a new data structure. Default: true.
• path: deepget/deepset key path.
• sep: deepget/deepset key path separator. Default: '.'.

For non-numeric arrays, provide an accessor function for accessing array values.

var data = [
	['beep', -10],
	['boop', -1],
	['bip', 0],
	['bap', 1],
	['baz', 10]
];

function getValue( d, i ) {
	return d[ 1 ];
}

var out = signum( data, {
	'accessor': getValue
});
// returns [ -1, -1, 0, 1, 1 ]

To deepset an object array, provide a key path and, optionally, a key path separator.

var data = [
	{'x':[0,-10]},
	{'x':[1,-1]},
	{'x':[2,0]},
	{'x':[3,1]},
	{'x':[4,10]}
];

var out = signum( data, 'x|1', '|' );
/*
	[
		{'x':[0,-1]},
		{'x':[1,-1]},
		{'x':[2,0]},
		{'x':[3,1]},
		{'x':[4,1]}
	]
*/

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

By default, the function returns a new data structure. To mutate the input data structure (e.g., when input values can be discarded or when optimizing memory usage), set the copy option to false.

var data,
	bool,
	mat,
	out,
	i;

var data = [ -10, -1, 0, 1, 10 ];

var out = signum( data, {
	'copy': false
});
// returns [ -1, -1, 0, 1, 1 ]

bool = ( data === out );
// returns true

data = new Int8Array( 6 );
for ( i = 0; i < 6; i++ ) {
	data[ i ] = i - 3;
}
mat = matrix( data, [3,2], 'int8' );
/*
	[ -3 -2
	  -1  0
	   1  2 ]
*/

out = signum( mat, {
	'copy': false
});
/*
	[ -1 -1
	  -1  0
	   1  1 ]
*/

bool = ( mat === out );
// returns true

When provided a typed array or matrix, the output data structure is of type int8. If the copy option is false, the original data type of the typed array or matrix is preserved.

Notes

Table of results:

Value | Sign
:---: | :---: | x > 0 | +1 x < 0 | -1 0 | 0 -0 | -0 NaN | NaN

The above results are compatible with an ECMAScript 6 proposal from Mozilla, which would extend the Math object to include the method Math.sign(). Currently, only Mozilla implements this proposal.

Examples

var matrix = require( 'dstructs-matrix' ),
	signum = require( 'compute-signum' );

var data,
	mat,
	out,
	tmp,
	i;

// Plain arrays...
data = new Array( 10 );
for ( i = 0; i < data.length; i++ ) {
	data[ i ] = Math.random()*20 - 10;
}
out = signum( data );

// Object arrays (accessors)...
function getValue( d ) {
	return d.x;
}
for ( i = 0; i < data.length; i++ ) {
	data[ i ] = {
		'x': data[ i ]
	};
}
out = signum( data, {
	'accessor': getValue
});

// Deep set arrays...
for ( i = 0; i < data.length; i++ ) {
	data[ i ] = {
		'x': [ i, data[ i ].x ]
	};
}
out = signum( data, {
	'path': 'x/1',
	'sep': '/'
});

// Typed arrays...
data = new Int32Array( 10 );
for ( i = 0; i < data.length; i++ ) {
	data[ i ] = Math.random()*20 - 10;
}
tmp = signum( data );
out = '';
for ( i = 0; i < data.length; i++ ) {
	out += tmp[ i ];
	if ( i < data.length-1 ) {
		out += ',';
	}
}

// Matrices...
mat = matrix( data, [5,2], 'int32' );
out = signum( mat );

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

License

MIT license.

Copyright

Copyright © 2014-2015. The Compute.io Authors.