Less Than

Computes an element-wise comparison (less than) of an array.

Installation

$ npm install compute-lt

For use in the browser, use browserify.

Usage

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

lt( arr, x[, opts] )

Computes an element-wise comparison (less than) for each input array element. x may either be an array of equal length or a single value (number or string).

The function returns an array with a length equal to that of the input array. Each output array element is either 0 or 1. A value of 1 means that an element is less than a compared value and 0 means that an element is not less than a compared value.

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

// Single comparison value:
out = lt( arr, 4 );
// returns [ 0, 1, 0, 1, 1 ]

// Array of comparison values:
out = lt( arr, [ 6, 2, 6, 7, 3 ] );
// returns [ 1, 0, 0, 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 = lt( arr, 4, {
	'copy': false
});
// returns [ 0, 1, 0, 1, 1 ]

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

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 = lt( data, 4, {
	'accessor': getValue
});
// returns [ 0, 1, 0, 1, 1 ]

When comparing 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 = lt( data, arr, {
	'accessor': getValue
});
// returns [ 0, 1, 0, 1, 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 (comparison) input array.

Examples

var lt = require( 'compute-lt' ),
	sum = require( 'compute-sum' );

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

var out = lt( data, 50 );

// Count the number of values less than 50...
var count = sum( out );

console.log( 'Total: %d', count );

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. Athan Reines.