Subtract

Computes an element-wise subtraction.

Installation

$ npm install compute-subtract

For use in the browser, use browserify.

Usage

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

subtract( arr, x[, opts] )

Computes an element-wise subtraction. x may be either an array of equal length or a numeric value.

var arr = [ 2, 1, 4, 2 ],
	out;

out = subtract( arr, 1 );
// returns [ 1, 0, 3, 1 ]

out = subtract( arr, [ 1, 2, 3, 3 ] );
// returns [ 1, -1, 1, -1 ]

The function accepts the following options:

• copy: boolean indicating whether to return a new array. Default: true.
• accessor: accessor function for accessing values in object arrays.

To mutate the input array (e.g., when input values can be discarded or when optimizing memory usage), set the copy option to false.

var arr = [ 5, 3, 8, 3, 2 ];

var out = subtract( arr, 4, {
	'copy': false
});
// returns [ 1, -1, 4, -1, -2 ]

console.log( arr === out );
// returns true

Note: mutation is the array equivalent of a minus-equal (-=).

For object arrays, provide an accessor function for accessing array values.

var data = [
	['beep', 5],
	['boop', 3],
	['bip', 8],
	['bap', 3],
	['baz', 2]
];

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

var out = subtract( data, 4, {
	'accessor': getValue
});
// returns [ 1, -1, 4, -1, -2 ]

When subtracting values between two object arrays, provide an accessor function which accepts 3 arguments.

var data = [
	['beep', 5],
	['boop', 3],
	['bip', 8],
	['bap', 3],
	['baz', 2]
];

var arr = [
	{'x': 4},
	{'x': 5},
	{'x': 6},
	{'x': 5},
	{'x': 3}
];

function getValue( d, i, j ) {
	if ( j === 0 ) {
		return d[ 1 ];
	}
	return d.x;
}

var out = subtract( data, arr, {
	'accessor': getValue
});
// returns [ 1, -2, 2, -2, -1 ]

Note: j corresponds to the input array index, where j=0 is the index for the first input array and j=1 is the index for the second input array.

Examples

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

var data = new Array( 100 );
for ( var i = 0; i < data.length; i++ ) {
	data[ i ] = Math.round( Math.random()*100 );
}

var out = subtract( data, 10 );

console.log( out.join( '\n' ) );

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.