Absolute Value
===
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> Computes an element-wise [absolute value](https://en.wikipedia.org/wiki/Absolute_value).

The [absolute value](https://en.wikipedia.org/wiki/Absolute_value) is defined as

<div class="equation" align="center" data-raw-text="
    |x| = \begin{cases} x &amp; \textrm{if}\ x \geq 0 \\ -x &amp; \textrm{if}\ x < 0\end{cases}" data-equation="eq:absolute_value">
	<img src="https://cdn.rawgit.com/compute-io/abs/35f3f35f5a7ea712dc1e5bb5a4e8a9909ce76507/docs/img/eqn.svg" alt="Absolute value definition.">
	<br>
</div>


## Installation

``` bash
$ npm install compute-abs
```

For use in the browser, use [browserify](https://github.com/substack/node-browserify).


## Usage

``` javascript
var abs = require( 'compute-abs' );
```


#### abs( x[, opts] )

Computes an element-wise [absolute value](https://en.wikipedia.org/wiki/Absolute_value). `x` may be either a [`number`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number), an [`array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array), a [`typed array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Typed_arrays), or a [`matrix`](https://github.com/dstructs/matrix).


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

out = abs( 3 );
// returns 3

out = abs( -3 );
// returns 3

data = [ -2, 1, -3 ];
out = abs( data );
// returns [ 2, 1, 3 ]

data = new Int8Array( data );
out = abs( data );
// returns Float64Array( [2, 1, 3] )

data = new Int16Array( 6 );
for ( i = 0; i < 6; i++ ) {
	data[ i ] = i - 3;
}
mat = matrix( data, [3,2], 'int16' );
/*
	[ -3 -2
	  -1  0
	   1  2 ]
*/

out = abs( mat );
/*
	[ 3 2
	  1 0
	  1 2 ]
*/
```

The function accepts the following `options`:

* 	__accessor__: accessor `function` for accessing `array` values.
* 	__dtype__: output [`typed array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Typed_arrays) or [`matrix`](https://github.com/dstructs/matrix) data type. Default: `float64`.
*	__copy__: `boolean` indicating if the `function` should return a new data structure. Default: `true`.
*	__path__: [deepget](https://github.com/kgryte/utils-deep-get)/[deepset](https://github.com/kgryte/utils-deep-set) key path.
*	__sep__: [deepget](https://github.com/kgryte/utils-deep-get)/[deepset](https://github.com/kgryte/utils-deep-set) key path separator. Default: `'.'`.

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

``` javascript
var data = [
	[0,4],
	[1,-9],
	[2,16],
	[3,-25],
	[4,36]
];

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

var out = abs( data, {
	'accessor': getValue
});
// returns [ 4, 9, 16, 25, 36 ]
```

To [deepset](https://github.com/kgryte/utils-deep-set) an object `array`, provide a key path and, optionally, a key path separator.

``` javascript
var data = [
	{'x':[0,4]},
	{'x':[1,-9]},
	{'x':[2,16]},
	{'x':[3,-25]},
	{'x':[4,36]}
];

var out = abs( data, {
	'path': 'x|1',
	'sep': '|'
});
/*
	[
		{'x':[0,4]},
		{'x':[1,9]},
		{'x':[2,16]},
		{'x':[3,25]},
		{'x':[4,36]}
	]
*/

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

By default, when provided a [`typed array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Typed_arrays) or [`matrix`](https://github.com/dstructs/matrix), the output data structure is `float64` in order to preserve precision. To specify a different data type, set the `dtype` option (see [`matrix`](https://github.com/dstructs/matrix) for a list of acceptable data types).

``` javascript
var data, out;

data = new Float32Array( [ -0.1, 0.1, 10, -10] );

out = abs( data, {
	'dtype': 'int32'
});
// returns Int32Array( [0, 0, 10, 10] )

// Works for plain arrays, as well...
out = abs( [ -0.1, 0.1, 10, -10], {
	'dtype': 'uint8'
});
// returns Uint8Array( [0, 0, 10, 10] )
```

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`.

``` javascript
var data,
	bool,
	mat,
	out,
	i;

data = [ -4, 9, -16 ];

out = abs( data, {
	'copy': false
});
// returns [ 4, 9, 16 ]

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

data = new Int16Array( 6 );
for ( i = 0; i < 6; i++ ) {
	data[ i ] = i - 3;
}
mat = matrix( data, [3,2], 'int16' );
/*
	[ -3 -2
	  -1  0
	   1  2 ]
*/

out = abs( mat, {
	'copy': false
});
/*
	[ 3 2
	  1 0
	  1 2 ]
*/

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


## Notes

*	If an element is __not__ a numeric value, the element's [absolute value](https://en.wikipedia.org/wiki/Absolute_value) is `NaN`.

	``` javascript
	var data, out;

	out = abs( null );
	// returns NaN

	out = abs( true );
	// returns NaN

	out = abs( {'a':'b'} );
	// returns NaN

	out = abs( [ -1, null, -2 ] );
	// returns [ 1, NaN, 2 ]

	function getValue( d, i ) {
		return d.x;
	}
	data = [
		{'x':4},
		{'x':-9},
		{'x':16},
		{'x':null},
		{'x':-25},
		{'x':36}
	];

	out = abs( data, {
		'accessor': getValue
	});
	// returns [ 4, 9, 16, NaN, 25, 36 ]

	out = abs( data, {
		'path': 'x'
	});
	/*
		[
			{'x':4},
			{'x':9},
			{'x':16},
			{'x':NaN},
			{'x':25},
			{'x':36}
		]
	*/
	```

*	Be careful when providing a data structure which contains non-numeric elements and specifying an `integer` output data type, as `NaN` values are cast to `0`.

	``` javascript
	var out = abs( [ -1, null, -2 ], {
		'dtype': 'int8'
	});
	// returns Int8Array( [1, 0, 2] );
	```


## Examples

``` javascript
var matrix = require( 'dstructs-matrix' ),
	abs = require( 'compute-abs' );

var data,
	mat,
	out,
	tmp,
	i;

// Plain arrays...
data = new Array( 10 );
for ( i = 0; i < data.length; i++ ) {
	data[ i ] = Math.random()*20 - 100;
}
out = abs( data );

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

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

// Typed arrays...
data = new Int32Array( 10 );
for ( i = 0; i < data.length; i++ ) {
	data[ i ] = Math.random()*20 - 100;
}
tmp = abs( 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 = abs( mat );

// Matrices (custom output data type)...
out = abs( mat, {
	'dtype': 'uint8'
});
```

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

``` bash
$ node ./examples/index.js
```



## Tests

### Unit

Unit tests use the [Mocha](http://mochajs.org) test framework with [Chai](http://chaijs.com) assertions. To run the tests, execute the following command in the top-level application directory:

``` bash
$ make test
```

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


### Test Coverage

This repository uses [Istanbul](https://github.com/gotwarlost/istanbul) as its code coverage tool. To generate a test coverage report, execute the following command in the top-level application directory:

``` bash
$ make test-cov
```

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

``` bash
$ make view-cov
```


---
## License

[MIT license](http://opensource.org/licenses/MIT).


## Copyright

Copyright &copy; 2014-2015. The [Compute.io](https://github.com/compute-io) Authors.


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[npm-url]: https://npmjs.org/package/compute-abs

[travis-image]: http://img.shields.io/travis/compute-io/abs/master.svg
[travis-url]: https://travis-ci.org/compute-io/abs

[coveralls-image]: https://img.shields.io/coveralls/compute-io/abs/master.svg
[coveralls-url]: https://coveralls.io/r/compute-io/abs?branch=master

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[dependencies-url]: https://david-dm.org/compute-io/abs

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[dev-dependencies-url]: https://david-dm.org/dev/compute-io/abs

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[github-issues-url]: https://github.com/compute-io/abs/issues