compute-abs

Absolute Value
===
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> Computes an element-wise absolute value.

The absolute value is defined as

Installation

`` bash
$ npm install compute-abs
`

For use in the browser, use browserify.

Usage

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


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

Computes an element-wise absolute value. x may be either a number, an array, a typed array, or a 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 or matrix data type. Default: float64.
* __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.

` 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 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 or matrix, the output data structure is float64 in order to preserve precision. To specify a different data type, set the dtype option (see 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 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

$3

Unit tests use the Mocha test framework with Chai 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.

$3

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:

` 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.

Copyright

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

[npm-image]: http://img.shields.io/npm/v/compute-abs.svg
[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

[dependencies-image]: http://img.shields.io/david/compute-io/abs.svg
[dependencies-url]: https://david-dm.org/compute-io/abs

[dev-dependencies-image]: http://img.shields.io/david/dev/compute-io/abs.svg
[dev-dependencies-url]: https://david-dm.org/dev/compute-io/abs

[github-issues-image]: http://img.shields.io/github/issues/compute-io/abs.svg
[github-issues-url]: https://github.com/compute-io/abs/issues